Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 179.8	$ 140.0	$ 288.6	$ 231.4
Available-for-sale securities:
Unrealized gains net of tax benefit of $0.4 and provision of $0.3 during the three and six months ended June 30, 2017, respectively, and tax benefit of $0.6 and $0.7 for the corresponding periods of the fiscal year ended December 31, 2016 (fiscal 2016), respectively	0.1	1.7	1.6	6.0
Reclassification adjustment for realized net gains included in net income, net of tax provision of zero for each period of fiscal 2017 and net of tax provisions of $0.5 for each period of the corresponding periods of fiscal 2016	0.0	(1.0)	(0.1)	(0.8)
Net change on available-for-sale securities, net of taxes	0.1	0.7	1.5	5.2
Cash flow hedges:
Unrealized gains net of tax provision of $0.8 and $2.5, for the three and six months ended June 30, 2017, respectively, and tax provisions of $0.1 and $0.6 for the corresponding periods of fiscal 2016, respectively	3.0	1.4	8.3	3.9
Reclassification adjustment for realized net (gains) losses included in net income, net of tax provisions of $0.6 and $0.9 during the three and six months ended June 30, 2017, respectively, and tax provisions of $0.3 and $0.1 for the corresponding periods of fiscal 2016, respectively	(1.0)	(1.2)	0.1	(0.1)
Net change on cash flow hedges, net of taxes	2.0	0.2	8.4	3.8
Change in foreign currency translation adjustments	3.0	2.2	10.9	5.8
Other comprehensive income, net of tax	5.1	3.1	20.8	14.8
Comprehensive income	$ 184.9	$ 143.1	$ 309.4	$ 246.2