Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Taxes
Provision for income taxes	$ (63.6)	$ (75.3)	$ (134.6)	$ (139.2)
Effective tax rate (as a percent)	20.10%	26.50%	21.90%	27.50%
Impact of acquisition-related expenses on the effective tax rate (in basis points)				1.00%
Liability for unrecognized tax benefits, including penalties and interest, which if recognized would impact the effective tax rate	$ 133.7		$ 133.7
Unrecognized tax benefits that could change in the next twelve-month period	5.7		5.7
Impact of ASU 2016-09
Income Taxes
Provision for income taxes	$ 21.2		$ 29.2
Impact of tax benefits related to stock-based compensation (in basis points)	6.60%		4.70%