Gains and Losses on Derivatives Designated as Hedging Instruments, Cash Flow Hedging (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments Gain Loss [Line Items]
Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	$ 0	$ 0
Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion)	0	(0.1)
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	(0.4)	(0.6)
Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion)	0	(0.1)
Cash Flow Hedging [Member] | Interest Expense [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	$ (0.4)	$ (0.6)