Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Taxes
Effective tax rate (as a percent)	26.50%	26.40%
Effective tax rate excluding the net impact of separately stated acquisition-related expenses (as a percent)	26.50%	26.50%
Liability for unrecognized tax benefits, including penalties and interest, which if recognized would impact the effective tax rate	$ 18.8
Unrecognized tax benefits, anticipated adjustment for changing facts and circumstances, over the next twelve month period	$ 1.0