Consolidated Statements of Comprehensive Income Parenthetical - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Tax (provision) on change in unrealized gains on available-for-sale securities	$ (6.5)	$ (29.5)	$ (37.9)
Tax provision on reclassification adjustment for realized net gains on available-for-sale securities included in net income	0.0	61.8	0.4
Tax (provision) benefit on change in unrealized (losses) gains on cash flow hedges	(0.4)	(0.7)	1.7
Tax provision (benefit) on reclassification adjustment for realized losses (gains) included in net income	$ 0.0	$ 1.1	$ (0.8)