Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 197.7	$ 103.6	$ 435.9	$ 435.3
Available-for-sale securities:
Unrealized (losses) gains on available-for-sale securities, net of tax (provisions) benefit of ($3.7) and ($2.1) during the three and nine months ended September 30, 2015, respectively, and $2.0 and ($26.2) for the corresponding periods of the fiscal year ended December 31, 2014 (fiscal 2014), respectively	(3.6)	(4.4)	4.6	44.0
Reclassification adjustment for realized net gains on available-for-sale securities included in net income, net of tax provisions of zero during the three and nine months ended September 30, 2015, respectively, and $0.1 and $60.5 for the corresponding periods of fiscal 2014, respectively	(0.1)	(0.2)	(0.6)	(104.0)
Net change on available-for-sale securities, net of taxes	(3.7)	(4.6)	4.0	(60.0)
Cash flow hedges:
Unrealized (losses) gain on cash flow hedges, net of tax benefit (provisions) of $0.5 and ($0.2) during the three and nine months ended September 30, 2015, respectively, and zero and ($1.3) for the corresponding periods of fiscal 2014, respectively	(1.4)	(2.8)	(5.4)	0.4
Reclassification adjustment for realized net losses (gains) on cash flow hedges included in net income, net of tax (benefit) provisions of ($0.1) and zero during the three and nine months ended September 30, 2015, respectively, and $0.5 and $0.8 for the corresponding periods of fiscal 2014, respectively	1.8	(1.0)	8.7	(4.2)
Net change on cash flow hedges, net of taxes	0.4	(3.8)	3.3	(3.8)
Change in foreign currency translation adjustments	(8.8)	(7.7)	(12.9)	(3.8)
Other comprehensive loss, net of tax	(12.1)	(16.1)	(5.6)	(67.6)
Comprehensive income	$ 185.6	$ 87.5	$ 430.3	$ 367.7