Equity - Components of Accumulated Other Comprehensive (Loss) Income, Net of Tax (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications	$ 16.4
Amount reclassified from accumulated other comprehensive income (loss)	(4.2)
Reclassification of tax effects upon adoption of ASU No. 2018-02	5.7
Other comprehensive income, net	17.9
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	(5.4)
Balance as of March 31, 2018	12.5
Unrealized Gains on Available-for- Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	19.0
Other comprehensive income before reclassifications	(2.0)
Amount reclassified from accumulated other comprehensive income (loss)	0.9
Reclassification of tax effects upon adoption of ASU No. 2018-02	5.0
Other comprehensive income, net	3.9
Balance as of March 31, 2018	22.9
Unrealized (Losses) Gains on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	6.0
Other comprehensive income before reclassifications	13.1
Amount reclassified from accumulated other comprehensive income (loss)	(5.1)
Reclassification of tax effects upon adoption of ASU No. 2018-02	0.7
Other comprehensive income, net	8.7
Balance as of March 31, 2018	14.7
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	(30.4)
Other comprehensive income before reclassifications	5.3
Amount reclassified from accumulated other comprehensive income (loss)	0.0
Reclassification of tax effects upon adoption of ASU No. 2018-02	0.0
Other comprehensive income, net	5.3
Balance as of March 31, 2018	$ (25.1)