Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 633.7	$ (334.3)	$ 439.8
Available-for-sale securities:
Unrealized gains on available-for-sale securities, net of tax (provision) of ($6.5), ($29.5) and ($37.9) for 2015, 2014 and 2013, respectively	9.1	48.7	65.1
Reclassification adjustment for realized net gains on available-for- sale securities included in net income (loss), net of tax provision of zero, $61.8 and $0.4 for 2015, 2014 and 2013, respectively	(0.5)	(106.5)	(1.0)
Net change on available-for-sale securities, net of taxes	8.6	(57.8)	64.1
Cash flow hedges:
Unrealized (losses) gain on cash flow hedges, net of tax (provision) benefit of ($0.4), ($0.7) and $1.7 for 2015, 2014 and 2013, respectively	(6.7)	(4.1)	0.7
Reclassification adjustment for realized loss (gains) on cash flow hedges included in net income (loss), net of tax provision (benefit) of zero, $1.1 and ($0.8) for 2015, 2014 and 2013, respectively	9.6	(2.3)	(1.5)
Net change on cash flow hedges, net of taxes	2.9	(6.4)	(0.8)
Change in foreign currency translation adjustments	(16.9)	(14.2)	(3.4)
Other comprehensive (losses) income, net of tax	(5.4)	(78.4)	59.9
Comprehensive income (loss)	$ 628.3	$ (412.7)	$ 499.7