Comprehensive Income (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Comprehensive Income (Loss) [Line Items]
Other comprehensive income, reclassification adjustments on derivatives, net of tax	$ 0	$ 2.6	$ 0
Defined benefit plan adjustment, before tax		14.0
Defined benefit plan adjustment, after tax	0	8.5	0
Interest Expense [Member] | Interest Rate Collars And Swaps [Member]
Comprehensive Income (Loss) [Line Items]
Other comprehensive income, reclassification adjustments on derivatives, before tax		4.3
Other comprehensive income, reclassification adjustments on derivatives, net of tax		$ 2.6