Derivative Instruments and Hedging Activities - Impact of Changes in Fair Value of Interest Rate Swaps and Underlying Hedged Items on Results of Operations (Detail) (Interest Rate Swaps [Member], Interest Expense [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Swap [Member]
Derivatives, Fair Value [Line Items]
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments	$ (1)	$ 35	$ 6
Fixed-Rate Debt [Member]
Derivatives, Fair Value [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge	$ 1	$ (35)	$ (6)