Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 99.3	$ 223.8	$ 176.6	$ 374.7
Available-for-sale debt securities:
Change in net unrealized gains and losses, net of tax (provision) of zero and ($0.8) during the three and nine months ended September 30, 2019, respectively, and tax (provision) benefit of ($0.3) and $0.9 for the comparable periods in 2018, respectively	0.0	0.9	3.8	(0.6)
Net realized losses reclassified into net income, net of tax provisions of zero for each period	(0.1)	0.0	(0.1)	0.9
Net change on available-for-sale debt securities, net of tax	(0.1)	0.9	3.7	0.3
Cash flow hedges:
Change in net unrealized gains and losses, net of tax provisions of $0.2 and $1.3 during the three and nine months ended September 30, 2019, respectively, and tax benefits of $1.5 and $2.7 for the comparable periods in 2018, respectively	(12.6)		(12.3)
Change in net unrealized gains and losses, net of tax provisions of $0.2 and $1.3 during the three and nine months ended September 30, 2019, respectively, and tax benefits of $1.5 and $2.7 for the comparable periods in 2018, respectively		(4.6)		(5.9)
Net realized (gains) and losses reclassified into net income, net of tax provisions of $0.7 and $1.5 during the three and nine months ended September 30, 2019, respectively, and tax (benefit) provision of ($0.5) and $0.3 for the comparable periods in 2018, respectively	1.5		3.0
Net realized (gains) and losses reclassified into net income, net of tax provisions of $0.7 and $1.5 during the three and nine months ended September 30, 2019, respectively, and tax (benefit) provision of ($0.5) and $0.3 for the comparable periods in 2018, respectively		2.6		(5.5)
Net change on cash flow hedges, net of tax	(11.1)		(9.3)
Net change on cash flow hedges, net of tax		(2.0)		(11.4)
Change in foreign currency translation adjustments	(4.3)	(7.0)	(3.0)	(13.7)
Other comprehensive (loss) income, net of tax	(15.5)	(8.1)	(8.6)	(24.8)
Comprehensive income	$ 83.8	$ 215.7	$ 168.0	$ 349.9