Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Effective income tax rate	16.10%	20.30%	18.40%	17.00%
Combined federal and state statutory income tax rate			38.70%	38.90%
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 11.9		$ 11.9		$ 14.0
Accrued interest and penalties related to uncertain tax positions	2.3		2.3		4.1
Portion of unrecognized tax benefits, including accrued interest and penalties, that if recognized, would impact the effective tax rate	12.1		12.1		15.2
Reasonably possible decrease in unrecognized tax benefits, lower bound	2.0		2.0
Reasonably possible decrease in unrecognized tax benefits, upper bound	4.0		4.0
Other long-term liabilities, net [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefits	0.9		0.9		1.5
Accrued and other current liabilities [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefits	1.0		1.0		2.5
Deferred income tax liabilities [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 10.0		$ 10.0		$ 10.0