Location and Amounts of Gains and Losses on Derivative Instrument Designated as Fair Value Hedge (Detail) (Interest rate swap contract, Interest Expense, USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Interest rate swap contract | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
(Loss)/Gain Recognized on Swap	$ (2.1)	$ 1.6	$ (3.2)	$ 1.5
Gain/Loss Recognized on Long-Term Debt	$ 2.1	$ (1.6)	$ 3.2	$ (1.5)