Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 110.6	$ 91.0
Available-for-sale securities:
Change in unrealized gains on available-for-sale securities, net of tax provision of ($22.1) for 2014	38.1	(0.2)	[1]
Reclassification adjustment for realized net gains on available-for-sale securities included in net income, net of tax provision of $60.3 for 2014	(103.5)	(0.4)	[1]
Net change in unrealized gains on available-for-sale securities	(65.4)	(0.6)	[1]
Cash flow hedges:
Change in unrealized gains on cash flow hedges, net of tax provision of ($0.6) for 2014	2.1	(2.1)	[1]
Reclassification adjustment for realized net gains on cash flow hedges included in net income, net of tax benefit of ($0.1) for 2014	(1.1)	(1.4)	[1]
Net change in unrealized gains on cash flow hedges, net of taxes	1.0	(3.5)	[1]
Change in foreign currency translation adjustments	1.7	(5.8)
Other comprehensive loss, net of tax	(62.7)	(9.9)
Comprehensive income	$ 47.9	$ 81.1

[1] Taxes related to available-for-sale securities and cash flow hedges were not material for 2013.