Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 34.4	$ 108.8
Available-for-sale debt securities:
Unrealized (loss) gain, net of tax benefit of $1.4 and tax provision $0.7, respectively	(2.0)	1.5
Reclassification adjustment for realized net loss (gain) included in net income, net of tax provisions of zero for each period	0.9	(0.1)
Net change on available-for-sale debt securities, net of tax	(1.1)	1.4
Cash flow hedges:
Unrealized gains, net of tax provisions of $0.3 and $1.7, respectively	13.1	5.3
Reclassification adjustment for realized net (gain) loss included in net income, net of tax provisions of $0.6 and $0.3, respectively	(5.1)	1.1
Net change on cash flow hedges, net of tax	8.0	6.4
Change in foreign currency translation adjustments	5.3	7.9
Other comprehensive income, net of tax	12.2	15.7
Comprehensive income	$ 46.6	$ 124.5