Change in the Fair Value for Interest Rate Contracts and the Related Hedged Items (Detail) (Fair Value Hedging, Interest Rate Contract, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest Expense Long Term Debt [Member]
Derivatives, Fair Value [Line Items]
Increase Decrease In Fair Value Of Interest Rate Fair Value Hedging Instruments	$ (104)	$ 220	$ 167
Increase Decrease In Fair Value Of Hedged Item In Interest Rate Fair Value Hedge	107	(227)	(168)
Interest Expense Deposits [Member]
Derivatives, Fair Value [Line Items]
Increase Decrease In Fair Value Of Interest Rate Fair Value Hedging Instruments			6
Increase Decrease In Fair Value Of Hedged Item In Interest Rate Fair Value Hedge			$ (6)