Equity, Accumulated Other Comprehensive Income, Net of Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications	$ 39.2	$ (15.8)	$ (14.5)
Amount reclassified from accumulated other comprehensive loss	(7.3)	(2.3)	9.1
Other comprehensive loss, net	31.9	(18.1)	(5.4)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Balance at beginning of period	(37.3)	(19.2)	(13.8)
Balance at end of period	(5.4)	(37.3)	(19.2)
Unrealized Gains on Available-for- Sale Securities
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Balance at beginning of period	16.6	17.0	8.4
Other comprehensive income (loss) before reclassifications	4.5	0.8	9.1
Amount reclassified from accumulated other comprehensive loss	(2.1)	(1.2)	(0.5)
Other comprehensive loss, net	2.4	(0.4)	8.6
Balance at end of period	19.0	16.6	17.0
Unrealized Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Balance at beginning of period	(4.5)	(1.3)	(4.2)
Other comprehensive income (loss) before reclassifications	15.7	(2.1)	(6.7)
Amount reclassified from accumulated other comprehensive loss	(5.2)	(1.1)	9.6
Other comprehensive loss, net	10.5	(3.2)	2.9
Balance at end of period	6.0	(4.5)	(1.3)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Balance at beginning of period	(49.4)	(34.9)	(18.0)
Other comprehensive income (loss) before reclassifications	19.0	(14.5)	(16.9)
Amount reclassified from accumulated other comprehensive loss	0.0	0.0	0.0
Other comprehensive loss, net	19.0	(14.5)	(16.9)
Balance at end of period	$ (30.4)	$ (49.4)	$ (34.9)