Income Taxes (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Provision at the U.S. statutory rate of 35%	$ 111.2	$ 96.0	$ 70.6
U.S. statutory rate	35.00%	35.00%	35.00%
Increase (reduction) in tax expense resulting from:
State income tax, net of federal income tax benefit	8.8	7.1	5.9
Other permanent items	(8.2)	(6.4)	(3.1)
Research tax credit	0	(0.5)	0
Change in unrecognized tax benefits	0.2	0.7	(5.1)
Change in valuation allowance	0.2	0.7	2.3
Foreign taxes at rates other than 35% and miscellaneous other	(2.7)	(3.2)	(3.9)
Total income tax provision	$ 109.5	$ 94.4	$ 66.7