Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 223.8	$ 165.7	$ 374.7	$ 454.3
Available-for-sale debt securities:
Unrealized gains (losses) net of tax provision of $0.3 and benefit of $0.9 during the three and nine months ended September 30, 2018, respectively, and tax benefits of $0.5 and $0.2 for the corresponding periods of the fiscal year ended December 31, 2017 (fiscal 2017), respectively	0.9	(0.2)	(0.6)	1.4
Reclassification adjustment for realized net (losses) gains included in net income, net of tax provisions of zero for the three and nine months ended September 30, 2018, respectively, and net of tax provisions of $0.9 for each of the corresponding periods of fiscal 2017	0.0	(1.9)	0.9	(2.0)
Net change on available-for-sale debt securities, net of tax	0.9	(2.1)	0.3	(0.6)
Cash flow hedges:
Unrealized (losses) gains net of tax benefits of $1.5 and $2.7 during the three and nine months ended September 30, 2018, respectively, and net of tax provisions of $0.5 and $3.0 for the corresponding periods of fiscal 2017, respectively	(4.6)	6.3	(5.9)	14.6
Reclassification adjustment for realized net losses (gains) included in net income, net of tax benefit of $0.5 and provision of $0.3 during the three and nine months ended September 30, 2018, respectively, and net of tax provisions of $0.8 and $1.7 for the corresponding periods of fiscal 2017, respectively	2.6	(2.5)	(5.5)	(2.4)
Net change on cash flow hedges, net of tax	(2.0)	3.8	(11.4)	12.2
Change in foreign currency translation adjustments	(7.0)	8.4	(13.7)	19.3
Other comprehensive (loss) income, net of tax	(8.1)	10.1	(24.8)	30.9
Comprehensive income	$ 215.7	$ 175.8	$ 349.9	$ 485.2