What was the change in the Computed expected income tax provision between 2017 and 2018?
{"Computed expected income tax provision": {"2019": 43.0, "2018": 232.6, "2017": 31.4}, "State income taxes, net of federal benefit": {"2019": -8.7, "2018": -1.3, "2017": -4.6}, "Foreign income taxed at lower than the federal rate": {"2019": -94.0, "2018": -208.8, "2017": -105.0}, "Impact of the Act - one-time transition tax, net of foreign tax credits": {"2019": 13.1, "2018": 653.7, "2017": "\u2014"}, "Impact of the Act - deferred tax effects, net of valuation allowance": {"2019": "\u2014", "2018": -136.7, "2017": "\u2014"}, "Global intangible low-taxed income": {"2019": 95.4, "2018": "\u2014", "2017": "\u2014"}, "Business realignment": {"2019": -90.6, "2018": "\u2014", "2017": "\u2014"}, "Increases related to current year tax positions": {"2019": 9.0, "2018": 32.0, "2017": 53.7}, "Decreases related to prior year tax positions (1)": {"2019": -75.1, "2018": -11.3, "2017": -36.3}, "Share-based compensation": {"2019": -13.3, "2018": -27.2, "2017": -25.0}, "Research and development tax credits": {"2019": -27.5, "2018": -17.0, "2017": -12.8}, "Intercompany prepaid tax asset amortization": {"2019": 5.2, "2018": 7.4, "2017": 7.9}, "Foreign exchange": {"2019": 4.6, "2018": -20.5, "2017": -1.7}, "Other": {"2019": -2.6, "2018": -0.5, "2017": 9.8}, "Change in valuation allowance": {"2019": -9.9, "2018": -20.5, "2017": 1.8}, "Total income tax provision (benefit)": {"2019": -151.4, "2018": 481.9, "2017": -80.8}}
computed_expected_income_tax_provision_2018 = df["Computed expected income tax provision"]["2018"]
computed_expected_income_tax_provision_2017 = df["Computed expected income tax provision"]["2017"]
answer = computed_expected_income_tax_provision_2018 - computed_expected_income_tax_provision_2017