Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 116.5	$ 179.8	$ 150.9	$ 288.6
Available-for-sale debt securities:
Unrealized gain (loss) net of tax provision of $0.2 and benefit of $1.2 during the three and six months ended June 30, 2018, respectively, and tax benefit of $0.4 and provision of $0.3 for the corresponding periods of the fiscal year ended December 31, 2017 (fiscal 2017), respectively	0.5	0.1	(1.5)	1.6
Reclassification adjustment for realized net loss (gain) included in net income, net of tax provisions of zero for each period	0.0	0.0	0.9	(0.1)
Net change on available-for-sale debt securities, net of tax	0.5	0.1	(0.6)	1.5
Cash flow hedges:
Unrealized (loss) gain net of tax benefits of $1.5 and $1.2 during the three and six months ended June 30, 2018, respectively, and tax provisions of $0.8 and $2.5 for the corresponding periods of fiscal 2017, respectively	(14.4)	3.0	(1.3)	8.3
Reclassification adjustment for realized net (gain) loss included in net income, net of tax provisions of $0.2 and $0.8 during the three and six months ended June 30, 2018, respectively, and net of tax provisions of $0.6 and $0.9 for the corresponding periods of fiscal 2017, respectively	(3.0)	(1.0)	(8.1)	0.1
Net change on cash flow hedges, net of tax	(17.4)	2.0	(9.4)	8.4
Change in foreign currency translation adjustments	(12.0)	3.0	(6.7)	10.9
Other comprehensive (loss) income, net of tax	(28.9)	5.1	(16.7)	20.8
Comprehensive income	$ 87.6	$ 184.9	$ 134.2	$ 309.4