Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Taxes
Effective tax rate (as a percent)	23.80%	28.70%
Impact of acquisition-related expenses on the effective tax rate (in basis points)		2.20%
Liability for unrecognized tax benefits, including penalties and interest, which if recognized would impact the effective tax rate	$ 139.8
Unrecognized tax benefits that could change in the next twelve-month period	$ 11.3