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		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest rate swap contract | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized on Swap	$ 1.0	$ 7.7	$ 2.5	$ 11.7
Loss Recognized on Long-Term Debt	$ (1.0)	$ (7.7)	$ (2.5)	$ (11.7)