Stockholders' Equity - Components of Accumulated Other Comprehensive Income, Net of Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 4,319.5	$ 3,379.4	$ 3,501.4
Other comprehensive income before reclassifications	0.8	3.0
Reclassified from accumulated other comprehensive income (loss)	(0.2)	(7.4)
Other comprehensive gains (losses)	0.6	(4.4)	(7.2)
Ending balance	5,777.8	4,319.5	3,379.4
Gains (Losses) on Hedge Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1.5	1.1
Other comprehensive income before reclassifications	4.1	7.8
Reclassified from accumulated other comprehensive income (loss)	(0.6)	(7.4)
Other comprehensive gains (losses)	3.5	0.4
Ending balance	5.0	1.5	1.1
Unrealized Gains (Losses) on Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4.2)	(0.2)
Other comprehensive income before reclassifications	(4.6)	(3.2)
Reclassified from accumulated other comprehensive income (loss)	0.2	(0.8)
Other comprehensive gains (losses)	(4.4)	(4.0)
Ending balance	(8.6)	(4.2)	(0.2)
Foreign Currency Translation Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3.3)	(2.1)
Other comprehensive income before reclassifications	2.0	(1.2)
Reclassified from accumulated other comprehensive income (loss)	0.0	0.0
Other comprehensive gains (losses)	2.0	(1.2)
Ending balance	(1.3)	(3.3)	(2.1)
Employee Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3.5)	(3.9)
Other comprehensive income before reclassifications	(0.7)	(0.4)
Reclassified from accumulated other comprehensive income (loss)	0.2	0.8
Other comprehensive gains (losses)	(0.5)	0.4
Ending balance	(4.0)	(3.5)	(3.9)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9.5)	(5.1)	2.1
Other comprehensive gains (losses)	0.6	(4.4)	(7.2)
Ending balance	$ (8.9)	$ (9.5)	$ (5.1)