Derivative Instruments Derivative Instruments Affecting the Consolidated Statements of Income (Details) (Cash Flow Hedging [Member], Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in OCI on Derivative (Effective Portion)	$ (0.5)	$ 0	$ (1.0)	$ 0
Amount of Gain/(Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(0.3)	0	(0.3)	(0.4)
Amount of Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0	0	0
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in OCI on Derivative (Effective Portion)	(0.5)	0	(1.0)	0
Interest Rate Swaps [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(0.3)	0	(0.3)	(0.4)
Amount of Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	$ 0	$ 0	$ 0	$ 0