Gains and Losses on Derivatives Designated as Hedging Instruments (Detail) (Cash Flow Hedging, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion)	$ (0.1)	$ (0.6)	$ (3.1)
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	(2.4)	(3.2)	(3.8)
Amount of Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion)	(0.1)	(0.6)	(3.1)
Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)		(0.2)	(1.0)
Amount of Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Interest income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	$ (2.4)	$ (3.0)	$ (2.8)