Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 99.1	$ 16.8	$ 288.0	$ 90.8
Available-for-sale securities:
Change in unrealized gains on available- for-sale securities	65.2	2.0	70.8	4.1
Reclassification adjustment for realized net gains on available-for-sale securities included in net income	(0.3)	(0.3)	(0.8)	(0.8)
Net change in unrealized gains on available-for-sale securities	64.9	1.7	70.0	3.3
Cash flow hedges:
Change in unrealized gains (losses) on cash flow hedges	0.7	4.3	(1.8)	6.9
Reclassification adjustment for realized net losses (gains) on cash flow hedges included in net income	0.6	2.4	(0.9)	7.4
Net change in unrealized gains (losses) on cash flow hedges	1.3	6.7	(2.7)	14.3
Change in foreign currency translation adjustments	4.1	5.2	(5.4)	5.3
Other comprehensive income, net of tax	70.3	13.6	61.9	22.9
Comprehensive income	$ 169.4	$ 30.4	$ 349.9	$ 113.7