Chief Justice Rehnquist
delivered the opinion of the Court.
Title 18 U. S. C. § 3585(b) provides that a defendant generally must “be given credit toward the service of a term of imprisonment for any time he has spent in official detention prior to the date the sentence commences.” Before the commencement of respondent’s federal sentence, a Federal Magistrate Judge “released” him on bail pursuant to the Bail Reform Act of 1984 and ordered him confined to a community treatment center. The question presented is whether respondent was in “official detention,” and thus entitled to a sentence credit under § 3585(b), during the time he spent at the treatment center. We hold that he was not.
On April 23, 1991, respondent Ziya Koray was arrested for laundering monetary instruments in violation of 18 U. S. C. § 1956(a)(1). On June 18, 1991, he pleaded guilty to that charge in the United States District Court for the District of Maryland. One week later, on June 25, 1991, a Federal Magistrate Judge entered a “release order” pursuant to 18 U. S. C. § 3142(c), ordering respondent released on bail, pending sentencing, into the custody of the Pretrial Services Agency. The order required that he be “confined to [the] premises” of a Volunteers of America community treatment center without “authoriz[ation] to leave for any reason unless accompanied” by a Government special agent. On October 22, 1991, the District Court sentenced respondent to 41 months’ imprisonment. Respondent remained at the Volunteers of America facility until November 25, 1991, the day he reported to the Allenwood Federal Prison Camp to serve his sentence.
Respondent requested the Bureau of Prisons (BOP or Bureau) to credit toward his sentence of imprisonment the approximately 150 days he spent at the Volunteers of America community treatment center between June 25 and November 25, 1991. Relying on its established policy, BOP refused to grant the requested credit. After exhausting his administrative remedies, respondent filed a petition for habeas corpus in the United States District Court for the Middle District of Pennsylvania seeking credit under 18 U. S. C. § 3585 for the time he spent at the community treatment center. The District Court denied the petition, finding that respondent’s stay at the center did not constitute “official detention” within the meaning of 18 U. S. C. § 3585(b).
The Court of Appeals for the Third Circuit reversed. 21 F. 3d 558 (1994). It acknowledged that the overwhelming majority of the Courts of Appeals “have concluded that section 3585 . . . does not require the Bureau to credit presen-tenced defendants whose bail conditions allowed them to be confined outside of Bureau of Prison[s] facilities.” Id., at 561. The court declined, however, to defer to the Bureau’s view — that time spent under highly restrictive conditions while “released” on bail is not “‘official detention’” under § 3585(b) because a “ ‘released’ ” defendant is not subject to the Bureau’s control. Id., at 562-565. Instead, the court reasoned that § 3585(b)’s “ ‘official detention’ ” language need not be read “as if it provided ‘official detention by the Attorney General or the Bureau of Prisons, ’ ” since “there is nothing in the statute which requires or suggests that a defendant must be under the detention of the Bureau,” and since “[a] court may ‘detain’ a person as ‘offlcial[ly]’ as the Attorney General.” Id., at 563-564. Concluding that “‘official detention’ for purposes of credit under 18 U. S. C. § 3585 includes time spent under conditions of jail-type confinement,” id., at 567, the Court of Appeals remanded the case for a determination whether respondent was in “jail-type confinement” during his stay at the Volunteers of America community treatment center.
We granted the Government’s petition for certiorari to resolve a conflict among the Courts of Appeals on the question whether a federal prisoner is entitled to credit against his sentence under § 3585(b) for time when he was “released” on bail pursuant to the Bail Reform Act of 1984. 513 U. S. 1106 (1995). We now reverse.
Title 18 U. S. C. § 3585 determines when a federal sentence of imprisonment commences and whether credit against that sentence must be granted for time spent in “official detention” before the sentence began. It states:
“Calculation of a term of imprisonment
“(a) Commencement of Sentence. — A sentence to a term of imprisonment commences on the date the defendant is received in custody awaiting transportation to, or arrives voluntarily to commence service of sentence at, the official detention facility at which the sentence is to be served.
“(b) Credit for Prior Custody — A defendant shall be given credit toward the service of a term of imprisonment for any time he has spent in official detention prior to the date the sentence commences—
“(1) as a result of the offense for which the sentence was imposed; or
“(2) as a result of any other charge for which the defendant was arrested after the commission of the offense for which the sentence was imposed;
“that has not been credited against another sentence.” 18 U. S. C. § 3585 (emphasis added).
In United States v. Wilson, 503 U. S. 329, 337 (1992), we specifically noted Congress’ use of the term “ ‘official detention’ ” in § 3585(b), but we had no occasion to rule on the meaning of that term. We must do so today.
The Government contends that the phrase “official detention” in § 3585(b) refers to a court order detaining a defendant and committing him to the custody of the Attorney General for confinement. Respondent, on the other hand, argues that the phrase “official detention” includes the restrictive conditions of his release on bail because the Federal Magistrate’s bail order was “official” and significantly curtailed his liberty. Viewing the phrase in isolation, it may be said that either reading is plausible. But it is a “fundamental principle of statutory construction (and, indeed, of language itself) that the meaning of a word cannot be determined in isolation, but must be drawn from the context in which it is used.” Deal v. United States, 508 U. S. 129, 132 (1993). After examining the phrase “official detention” in this light, we believe the Government’s interpretation is the correct one.
Section 3585(b) provides credit for time “spent in official detention prior to the date the sentence commences,” 18 U. S. C. § 3585(b) (emphasis added), thus making clear that credit is awarded only for presentence restraints on liberty. Because the Bail Reform Act of 1984, 18 U. S. C. § 3141 et seq., is the body of law that authorizes federal courts to place presentence restraints on a defendant’s liberty, see § 3142(a) (authorizing courts to impose restraints on the defendant “pending trial”); § 3143(a) (authorizing courts to impose restraints while the defendant “is waiting imposition or execution of sentence”), the “official detention” language of § 3585(b) must be construed in conjunction with that Act. This is especially so because the Bail Reform Act of 1984 was enacted in the same statute as the Sentencing Reform Act of 1984, of which § 3585 is a part. See Gozlon-Peretz v. United States, 498 U. S. 395, 407-408 (1991) (“It is not uncommon to refer to other, related legislative enactments when interpreting specialized statutory terms,” since Congress is presumed to have “legislated with reference to” those terms).
The Bail Reform Act of 1984 provides a federal court with two choices when dealing with a criminal defendant who has been “charged with an offense” and is awaiting trial, 18 U. S. C. § 3142(a), or who “has been found guilty of an offense and ... is awaiting imposition or execution of sentence,” 18 U. S. C. § 3143(a)(1) (1988 ed., Supp. V). The court may either (1) “release” the defendant on bail or (2) order him “detained” without bail. A court may “release” a defendant subject to a variety of restrictive conditions, including residence in a community treatment center. See §§ 3142(c) (1)(B)(i), (x), and (xiv). If, however, the court “finds that no condition or combination of conditions will reasonably assure the appearance of the person as required and the safety of any other person and the community,” § 3142(e), the court “shall order the detention of the person,” ibid., by issuing a “detention order” “direct[ing] that the person be committed to the custody of the Attorney General for confinement in a corrections facility,” § 3142(i)(2). Thus, under the language of the Bail Reform Act of 1984, a defendant suffers “detention” only when committed to the custody of the Attorney General; a defendant admitted to bail on restrictive conditions, as respondent was, is “released.” See Dawson v. Scott, 50 F. 3d 884, 889-890, and nn. 11-12 (CA11 1995); Moreland v. United States, 968 F. 2d 655, 659-660 (CA8), cert. denied, 506 U. S. 1028 (1992); 968 F. 2d, at 661-663 (Loken, J., concurring); United States v. Becak, 954 F. 2d 386, 388 (CA6), cert. denied, 504 U. S. 945 (1992).
Section 3585(a) and related sentencing provisions confirm this interpretation. Section 3585(a) provides that a federal sentence “commences” when the defendant is received for transportation to or arrives at “the official detention facility at which the sentence is to be served.” Title 18 U. S. C. §3621, in turn, provides that the sentenced defendant “shall be committed to the custody of the Bureau of Prisons,” § 3621(a), which “may designate any available penal or correctional facility . . . , whether maintained by the Federal Government or otherwise . . . , that the Bureau determines to be appropriate and suitable,” § 3621(b) (emphasis added). The phrase “official detention facility” in § 3585(a) therefore must refer to a correctional facility designated by the Bureau for the service of federal sentences, where the Bureau retains the discretion to “direct the transfer of a prisoner from one penal or correctional facility to another.” § 3621(b).
This reading of § 3585(a) is reinforced by other provisions governing the administration of federal sentences. For example, §3622 gives the Bureau authority to release a prisoner from the place of his imprisonment for a limited period to “participate in a training or educational program in the community while continuing in official detention at the prison facility,” § 3622(b), or to “work at paid employment in the community while continuing in official detention at the penal or correctional facility,” § 3622(c). Because the words “official detention” should bear the same meaning in subsections (a) and (b) of §3585 as they do in the above related sentencing statutes, see Estate of Cowart v. Nicklos Drilling Co., 505 U. S. 469, 479 (1992) (“[T]he basic canon of statutory construction [is] that identical terms within an Act bear the same meaning”), credit for time spent in “official detention” under § 3585(b) is available only to those defendants who were detained in a “penal or correctional facility,” § 3621(b), and who were subject to BOP’s control.
The context and history of § 3585(b) also support this view. As for context, § 3585(b) reduces a defendant’s “imprisonment” by the amount of time spent in “official detention” before his sentence, strongly suggesting that the period of presentence “detention” must be equivalent to the “imprisonment” itself. It would be anomalous to interpret § 3585(b) to require sentence credit for time spent confined in a community treatment center where the defendant is not subject to BOP’s control, since Congress generally views such a restriction on liberty as part of a sentence of “probation,” see 18 U. S. C. §§ 3563(b)(10), (12), and (14), or “supervised release,” see § 3583(d), rather than part of a sentence of “imprisonment.” See United States v. Zackular, 945 F. 2d 423, 425 (CA1 1991).
With respect to history, § 3585(b)’s predecessor, 18 U. S. C. §3568 (1982 ed.) (repealed), required the Attorney General to award sentence credit for “any days spent in custody in connection with the offense or acts for which sentence was imposed.” (Emphasis added.) The Courts of Appeals uniformly held that the phrase “in custody” did not allow sentence credit because of restrictions placed on a defendant’s liberty as a condition of release on bail. See Polakoff v. United States, 489 F. 2d 727, 730 (CA5 1974) (time spent on “highly restricted bond” not creditable as “‘custody’”); United States v. Robles, 563 F. 2d 1308, 1309 (CA9 1977) (“[T]ime spent on bail or on bond pending appeal is not time served ‘in custody’”), cert. denied, 435 U. S. 925 (1978); Ortega v. United States, 510 F. 2d 412, 413 (CA10 1975) (“‘custody’” refers to “actual custodial incarceration,” not “the time a criminal defendant is free on bond”); United States v. Peterson, 507 F. 2d 1191, 1192 (CADC 1974) (“ ‘in custody’ ” does “not refer to the stipulations imposed when a defendant is at large on conditional release”). In 1984, Congress enacted § 3585(b) and altered §3568 by, inter alia, “replac[ing] the term ‘custody’ with the term ‘official detention.’ ” Wilson, 503 U. S., at 337; see also 18 U. S. C. § 3585(b). In thus rewording the credit statute, however, nothing suggests that Congress disagreed with the Courts of Appeals’ rule denying credit to defendants who had been released on bail. To the contrary, Congress presumably made the change to conform the credit statute to the nomenclature used in related sentencing provisions, see 18 U. S. C. §§ 3585(a) and 3622, and in the Bail Reform Act of 1984. See Moreland, 968 F. 2d, at 662, and n. 5 (Loken, J., concurring).
The Bureau, as the agency charged with administering the credit statute, see Wilson, supra, at 334-335, likewise has interpreted § 3585(b)’s “official detention” language to require credit for time spent by a defendant under a § 3142(e) “detention order,” but not for time spent under a § 3142(c) “release order,” ho matter how restrictive the conditions. As we have explained, see supra, at 56-60, the Bureau’s interpretation is the most natural and reasonable reading of § 3585(b)’s “official detention” language. It is true that the Bureau’s interpretation appears only in a “Program Statement] ” — an internal agency guideline — rather than in “published regulations subject to the rigors of the Administrative Procedure] Act, including public notice and comment.” 21 F. 3d, at 562. But BOP’s internal agency guideline, which is akin to an “interpretive rule” that “do[es] not require notice and comment,” Shalala v. Guernsey Memorial Hospital, 514 U. S. 87, 99 (1995), is still entitled to some deference, cf. Martin v. Occupational Safety and Health Review Comm’n, 499 U. S. 144, 157 (1991), since it is a “permissible construction of the statute,” Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837, 843 (1984).
Respondent, as we have indicated, disagrees with the above interpretation of § 3585(b). He contends that the “plain meaning” of the phrase “official detention” includes the restrictive conditions of his confinement, even though he was released on bail. This contention is a plausible one if the phrase is read in isolation: respondent was subjected to restrictive conditions when released on bail, these conditions were imposed by a court order, and his sojourn in the community treatment center therefore amounted to “official detention.” But even without reference to the context of the language and the history of the statute, respondent’s is not the only plausible interpretation of the language; it would be too much to say that the statute “cannot bear the interpretation adopted by” the Bureau. Sullivan v. Everhart, 494 U. S. 83, 91-92 (1990). And in light of the foregoing textual and historical analysis, the initial plausibility of respondent’s reading simply does not carry the day.
Respondent also argues it is improper to focus on the release/detention dichotomy of the Bail Reform Act of 1984 to construe §3585(b)’s “official detention” language because a defendant “released” on bail may be subjected to conditions (under 18 U. S. C. § 3142(c)(1)(B)(xiv)) that are just as onerous as those faced by “detained” defendants. In addition, he asserts that his confinement as a “released” defendant in the Volunteers of America community treatment center constituted “official detention” because “sentenced” prisoners are deemed to be in “official detention” when BOP authorizes them to serve the last part of their sentences in a community treatment center, see U. S. Dept. of Justice, Bureau of Prisons Program Statement No. 7310.02 (Oct. 19, 1993) (interpreting 18 U. S. C. § 3624(c) to allow BOP to place sentenced prisoners in community corrections centers, since such centers meet 18 U. S. C. § 3621(b)’s definition of a “penal or correctional facility”), or to serve their sentences on educational or work release, see 18 U. S. C. §§ 3622(b) and (c).
It is quite true that under the Government’s theory a defendant “released” to a community treatment center could be subject to restraints which do not materially differ from those imposed on a “detained” defendant committed to the custody of the Attorney General, and thence assigned to a treatment center. But this fact does not undercut the remaining distinction that exists between all defendants committed to the custody of the Attorney General on the one hand, and all defendants released on bail on the other. Unlike defendants “released” on bail, defendants who are “detained” or “sentenced” always remain subject to the control of the Bureau. See Randall v. Whelan, 938 F. 2d 522, 525 (CA4 1991). This is an important distinction, as the identity of the custodian has both legal and practical significance. A defendant who is “released” is not in BOP’s custody, and he cannot be summarily reassigned to a different place of confinement unless a judicial officer revokes his release, see 18 U. S. C. § 3148(b), or modifies the conditions of his release, see § 3142(c)(3). A defendant who is “detained,” however, is completely subject to BOP’s control. And “[t]hat single factor encompasses a wide variety of restrictions.” Randall, supra, at 525. “Detained” defendants are subject to BOP’s disciplinary procedures; they are subject to summary reassignment to any other penal or correctional facility within the system, cf. Meachum v. Fano, 427 U. S. 215, 224-229 (1976); and, being in the legal custody of BOP, the Bureau has full discretion to control many conditions of their confinement. See Moody v. Daggett, 429 U. S. 78, 88, n. 9 (1976); Bell v. Wolfish, 441 U. S. 520, 544-548 (1979).
It may seem unwise policy to treat defendants differently for purposes of sentence credit under § 3585(b) when they are similarly situated in fact — the one is confined to a community treatment center after having been “detained” and committed to the Bureau’s custody, while the other is “released” to such a center on bail. But the alternative construction adopted by the Court of Appeals in this case has its own grave difficulties. To determine in each case whether a defendant “released” on bail was subjected to “jail-type confinement” would require a fact-intensive inquiry into the circumstances of confinement, an inquiry based on information in the hands of private entities not available to the Bureau as a matter of right. Even were such information more readily available, it seems certain that the phrase “jail-type confinement” would remain sufficiently vague and amorphous so that much the same kind of disparity in treatment for similarly situated defendants would arise. The Government’s construction of § 3585(b), on the other hand, provides both it and the defendant with clear notice of the consequences of a § 3142 “release” or “detention” order.
Respondent finally suggests that the rule of lenity requires adoption of the “jail-type confinement” test for purposes of calculating credit under § 3585(b) because “there is a split of authority in the Circuits concerning the reach of ‘official detention,’” Brief for Respondent 34, n. 13, and because there is ambiguity as to which forms of custody fall within the meaning of “‘official detention.’” See id., at 34. Respondent misconstrues the doctrine. A statute is not “ ‘ambiguous’ for purposes of lenity merely because” there is “a division of judicial authority” over its proper construction. Moskal v. United States, 498 U. S. 103, 108 (1990). The rule of lenity applies only if, “after seizing everything from which aid can be derived,” Smith v. United States, 508 U. S. 223, 239 (1993) (internal quotation marks and brackets omitted), we can make “no more than a guess as to what Congress intended.” Ladner v. United States, 358 U. S. 169, 178 (1958). That is not this case.
We hold that the time respondent spent at the Volunteers of America community treatment center while “released” on bail pursuant to the Bail Reform Act of 1984 was not “official detention” within the meaning of 18 U. S. C. § 3585(b). Respondent therefore was not entitled to a credit against his sentence of imprisonment. The judgment of the Court of Appeals is reversed, and the case is remanded for further proceedings consistent with this opinion.
It is so ordered.
Compare Dawson v. Scott, 50 F. 3d 884, 887-888 (CA11 1995) (time spent in halfway house and safe house while released on bond not creditable toward sentence); Moreland v. United States, 968 F. 2d 655, 657-660 (CA8) (en banc) (time spent in halfway house while released on bond not creditable toward sentence), cert. denied, 506 U. S. 1028 (1992); United States v. Edwards, 960 F. 2d 278, 282-283 (CA2 1992) (time spent in home confinement under electronic monitoring while released on bond not creditable toward sentence); Pinedo v. United States, 955 F. 2d 12, 14 (CA5 1992) (per curiam) (time spent on bail prior to trial not creditable toward sentence); United States v. Becak, 954 F. 2d 386, 387-388 (CA6) (time spent at mother’s house under conditions of release while released on bond not creditable toward sentence), cert. denied, 504 U. S. 945 (1992); United States v. Zackular, 945 F. 2d 423, 425 (CA1 1991) (time spent in home confinement prior to sentencing not creditable toward sentence); United States v. Insley, 927 F. 2d 185, 186 (CA4 1991) (time spent in home confinement while released on appeal bond not creditable toward sentence); United States v. Woods, 888 F. 2d 653, 655-656 (CA10 1989) (time spent at halfway house while released on bond not creditable toward sentence), cert. denied, 494 U. S. 1006 (1990), with Mills v. Taylor, 967 F. 2d 1397, 1400 (CA9 1992) (time spent in community treatment center while released on bail creditable toward sentence where “conditions of release approached] those of incarceration”).
Our task is strictly one of statutory interpretation. Respondent argued in the District Court that §3585 violated equal protection principles by treating pretrial defendants differently than postsentenced defendants. App. 23. The District Court rejected this argument. App. to Pet. for Cert. A-28. Respondent waived his equal protection argument in the Third Circuit, see 21 F. 3d 558, 559, n. 1 (1994), and he has not renewed it here. In an amicus curiae brief filed with this Court, University of Southern California Law Center’s Post-Conviction Justice Project raises a similar equal protection argument, see Brief for USC Law Center’s Post-Conviction Justice Project as Amicus Curiae 20-23, but that argument is not properly before the Court. See United Parcel Service, Inc. v. Mitchell, 451 U. S. 56, 60, n. 2 (1981) (noting that this Court does not decide issues raised by amici that were not decided by the court of appeals or argued by the.interested party); Bell v. Wolfish, 441 U. S. 520, 531, n. 13 (1979) (same).
See Comprehensive Crime Control Act of 1984, Pub. L. 98-473, Tit. II, 98 Stat. 1976. The provisions of the Comprehensive Crime Control Act of 1984 relating to bail are known as the Bail Reform Act of 1984. Pub. L. 98-473, Tit. II, ch. 1,98 Stat. 1976. The provisions relating to sentencing, including the credit provision of § 3585(b), are known as the Sentencing Reform Act of 1984. Pub. L. 98-473, Tit. II, ch. II, 98 Stat. 1987.
The Bureau’s view of § 3685(b) is explained in U. S. Dept. of Justice, Bureau of Prisons Program Statement No. 5880.28(c) (July 29, 1994), which reads as follows:
“Prior Custody Time Credit. The [Sentencing Reform Act] includes a new statutory provision, 18 U. S. C. § 3585(b), that pertains to ‘credit for prior custody’ and is controlling for making time credit determinations for sentences imposed under the SR A ...
“Definitions:
“Official detention. ‘Official detention’ is defined, for purposes of this policy, as time spent under a federal detention order. This also includes time spent under a detention order when the court has recommended placement in a less secure environment or in a community based program as a condition of presentence detention. A person under these circumstances remains in ‘official detention,’ subject to the discretion of the Attorney General and the U. S. Marshals Service with respect to the place of detention. Those defendants placed in a program and/or residence as a condition of detention are subject to removal and return to a more secure environment at the discretion of the Attorney General and the U. S. Marshals Service, and further, remain subject to prosecution for escape from detention for any unauthorized absence from the program/residence. Such a person is not similarly situated with persons conditionally released from detention with a requirement of program participation and/or residence.
“A defendant is not eligible for any credits while released from detention. Time spent in residence in a community corrections center as a result of the Pretrial Services Act of 1982 (18 U. S. C. § 3152-3164), or as a result of a condition of bail or bond (18 U. S. C. §3141-3143), is not creditable as presentence time. A condition of bail or bond which is ‘highly restrictive,’ and that includes ‘house arrest’, ‘electronic monitoring’ or ‘home confinement’; or such as requiring the defendant to report daily to the U. S. Marshal, U. S. Probation Service, or other person; is not considered as time in official detention. Such a defendant is not subject to the discretion of the U. S. Attorney General, the Bureau of Prisons, or the U. S. Marshals Service, regarding participation, placement, or subsequent return to a more secure environment, and therefore is not in a status which would indicate an award of credit is appropriate (see Randall v. Whelan, 938 F. 2d 522 (4th Cir. 1991) and U. S. v. Insley, 927 F. 2d 186 (4th Cir. 1991). Further, the government may not prosecute for escape in the case of an unauthorized absence in such cases, as the person has been lawfully released from ‘official detention.’” (Emphasis in original.)
In some cases, a defendant will be arrested, denied bail, and held in custody pursuant to state law, being turned over later to the Federal Government for prosecution. In these situations, BOP often grants credit under § 3585(b) for time spent in state custody, see, e.g., U. S. Dept. of Justice, Federal Bureau of Prisons, Operations Memorandum (Oct. 23, 1989); U. S. Dept. of Justice, Federal Bureau of Prisons, Sentence Computation Manual CCCA (1992 and Supp. 1994), even though the defendant was not subject to the control of BOP. These situations obviously are not governed by reference to a § 3142 “release” or “detention” order. But because the only question before us is whether a defendant is in “official detention” under § 3585(b) during the time he is “released” on bail pursu ant to the Bail Reform Act of 1984., we need not and do not rule here on the propriety of BOP’s decision to grant credit under § 3585(b) to a defendant who is denied bail pursuant to state law and held in the custody of state authorities. Thus, the dissent is simply wrong when it states that we have “adopt[ed] an interpretation that the Bureau of Prisons itself has rejected” by not allowing any ‘“credit for time spent in state custody.’” Post, at 67, 68.