Equity - Components of Accumulated Other Comprehensive (Loss) Income, Net of Tax (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	$ 4,823.2
Other comprehensive income before reclassifications	(11.5)
Amount reclassified from accumulated other comprehensive loss	2.9
Other comprehensive income, net	(8.6)
Balance	4,642.4
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(18.2)
Balance	(26.8)
Unrealized Gains/Losses on Available-for- Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	25.5
Other comprehensive income before reclassifications	3.8
Amount reclassified from accumulated other comprehensive loss	(0.1)
Other comprehensive income, net	3.7
Balance	29.2
Unrealized Gains/Losses on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(0.9)
Other comprehensive income before reclassifications	(12.3)
Amount reclassified from accumulated other comprehensive loss	3.0
Other comprehensive income, net	(9.3)
Balance	(10.2)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(42.8)
Other comprehensive income before reclassifications	(3.0)
Amount reclassified from accumulated other comprehensive loss	0.0
Other comprehensive income, net	(3.0)
Balance	$ (45.8)