What was the percentage change in balance as of December 31 between 2018 and 2019?
{"Balance as of January 1,": {"2019": 1004.8, "2018": 1126.2, "2017": 1091.3}, "Additions to redeemable noncontrolling interests": {"2019": 525.7, "2018": "\u2014", "2017": "\u2014"}, "Net income (loss) attributable to noncontrolling interests": {"2019": 35.8, "2018": -87.9, "2017": -33.4}, "Adjustment to noncontrolling interest redemption value": {"2019": -35.8, "2018": 86.7, "2017": "\u2014"}, "Adjustment to noncontrolling interest due to merger": {"2019": "\u2014", "2018": -28.1, "2017": "\u2014"}, "Purchase of redeemable noncontrolling interest": {"2019": -425.7, "2018": "\u2014", "2017": "\u2014"}, "Foreign currency translation adjustment attributable to noncontrolling interests": {"2019": -8.3, "2018": -92.1, "2017": 68.3}, "Balance as of December 31,": {"2019": 1096.5, "2018": 1004.8, "2017": 1126.2}}
balance_2019 = df["Balance as of December 31,"]["2019"]
balance_2018 = df["Balance as of January 1,"]["2019"]
answer = (balance_2019 - balance_2018) / balance_2018 * 100.0