Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 592.7	$ 633.7	$ (334.3)
Available-for-sale securities:
Unrealized gains net of tax benefit of $0.7, and provision of $6.5 and $29.5 for 2016, 2015, and 2014, respectively	0.8	9.1	48.7
Reclassification adjustment for realized net gains included in net income (loss), net of tax provision of $0.5, zero, and $61.8 for 2016, 2015, and 2014, respectively	(1.2)	(0.5)	(106.5)
Net change on available-for-sale securities, net of taxes	(0.4)	8.6	(57.8)
Cash flow hedges:
Unrealized loss net of tax provision of $0.8, $0.4, and $0.7 for 2016, 2015, and 2014, respectively	(2.1)	(6.7)	(4.1)
Reclassification adjustment for realized (gains) loss included in net income (loss), net of tax provision of $0.7, zero, and $1.1 for 2016, 2015, and 2014, respectively	(1.1)	9.6	(2.3)
Net change on cash flow hedges, net of taxes	(3.2)	2.9	(6.4)
Change in foreign currency translation adjustments	(14.5)	(16.9)	(14.2)
Other comprehensive loss, net of tax	(18.1)	(5.4)	(78.4)
Comprehensive income (loss)	$ 574.6	$ 628.3	$ (412.7)