Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Income Tax Expense (Benefit) [Abstract]
Net unrecognized tax benefit	$ 79.2		$ 79.2
Accrued interest on tax positions	0.1
Income tax examination, RAR asserted income tax deficiencies				13.1
Deferred tax assets	84.6
Income tax interest and penalties accrued	$ 1.5
Effective tax rate	19.30%	17.10%
U.S. federal statutory rate	35.00%