Consolidated Statements of Comprehensive Income Parenthetical - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Tax benefit (provision) on change in unrealized gains on available-for-sale securities	$ 0.7	$ (6.5)	$ (29.5)
Tax provision on reclassification adjustment for realized net gains on available-for-sale securities included in net income (loss)	(0.5)	0.0	(61.8)
Tax provision benefit on change in unrealized losses on cash flow hedges	(0.8)	(0.4)	(0.7)
Tax provision on reclassification adjustment for realized (gains) losses included in net income	$ (0.7)	$ 0.0	$ (1.1)