Comprehensive Income - Summary of the Tax Effects Allocated to each Component of Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Comprehensive Income (Loss), Pre-Tax
Foreign currency translation gain (loss)	$ (115.3)	$ (93.2)	$ (62.0)
Change in net realized and unrealized gain (loss) on derivative securities	0.3	2.3	0.6
Change in net unrealized gain (loss) on investment securities	(58.3)	34.8	5.6
Other comprehensive income (loss)	(173.3)	(56.1)	(55.8)
Other Comprehensive Income (Loss), Tax Benefit (Expense)
Foreign currency translation gain (loss)	0.0	0.0	0.0
Change in net realized and unrealized gain (loss) on derivative securities	(0.2)	(0.4)	(0.3)
Change in net unrealized gain (loss) on investment securities	23.1	(12.7)	(2.2)
Other comprehensive income (loss)	22.9	(13.1)	(2.5)
Other Comprehensive Income (Loss), Net of Tax
Foreign currency translation gain (loss)	(115.3)	(93.2)	(62.0)
Change in net realized and unrealized gain (loss) on derivative securities	0.1	1.9	0.3
Change in net unrealized gain (loss) on investment securities	(35.2)	22.1	3.4
Other comprehensive income (loss)	$ (150.4)	$ (69.2)	$ (58.3)