Condensed Consolidated Statements of Comprehensive Income Parentheticals (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Tax benefit (provision) on change in unrealized gains on available-for-sale securities	$ 5.4	$ (6.1)	$ 1.6	$ (28.2)
Tax provision on reclassification adjustment for realized net gains on available-for-sale securities included in net income	0.0	0.1	0.0	60.4
Tax provision on change in unrealized gains (losses) on cash flow hedges	0.4	0.7	0.7	1.3
Tax provision on reclassification adjustment for realized losses (gains) included in net income	$ 0.0	$ 0.4	$ 0.1	$ 0.3