Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 140.0	$ 158.0	$ 231.4	$ 238.2
Available-for-sale securities:
Unrealized gains on available-for-sale securities, net of tax benefit of $0.6 and $0.7 during the three and six months ended June 30, 2016, respectively, and $5.4 and $1.6 for the corresponding periods of the fiscal year ended December 31, 2015 (fiscal 2015), respectively	1.7	9.0	6.0	8.2
Reclassification adjustment for realized net gains on available-for-sale securities included in net income, net of tax provisions of $0.5 and $0.5 during the three and six months ended June 30, 2016, respectively, and zero for the corresponding periods of fiscal 2015	(1.0)	(0.3)	(0.8)	(0.5)
Net change on available-for-sale securities, net of taxes	0.7	8.7	5.2	7.7
Cash flow hedges:
Unrealized gains (loss) on cash flow hedges, net of tax provisions of $0.1 and $0.6 during the three and six months ended June 30, 2016, respectively, and $0.4 and $0.7 for the corresponding periods of fiscal 2015, respectively	1.4	2.4	3.9	(4.0)
Reclassification adjustment for realized net (gains) losses on cash flow hedges included in net income, net of tax provisions of $0.3 and $0.1 during the three and six months ended June 30, 2016, respectively, and zero and $0.1 for the corresponding periods of fiscal 2015, respectively	(1.2)	3.8	(0.1)	6.9
Net change on cash flow hedges, net of taxes	0.2	6.2	3.8	2.9
Change in foreign currency translation adjustments	2.2	7.0	5.8	(4.1)
Other comprehensive income, net of tax	3.1	21.9	14.8	6.5
Comprehensive income	$ 143.1	$ 179.9	$ 246.2	$ 244.7