Fair Value Option - Components of Gain on Instruments at Fair Value and Related Derivatives (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	$ (253)	[1]	$ (345)	[1]
Credit risk component	12		(156)
Total mark-to-market on financial instruments designated at fair value	(241)		(501)
Net realized loss on the financial instruments	(8)		(1)
Mark-to-market on the related derivatives	206		274
Net realized gain on the related long-term debt derivatives	16		16
Gain (loss) on instruments designated at fair value and related derivatives	(27)		(212)
Loans [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	0	[1]	1	[1]
Credit risk component	21		32
Total mark-to-market on financial instruments designated at fair value	21		33
Net realized loss on the financial instruments	(8)		(1)
Mark-to-market on the related derivatives	0		0
Net realized gain on the related long-term debt derivatives	0		0
Gain (loss) on instruments designated at fair value and related derivatives	13		32
Long-term Debt [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	63	[1]	83	[1]
Credit risk component	(42)		(221)
Total mark-to-market on financial instruments designated at fair value	21		(138)
Net realized loss on the financial instruments	0		0
Mark-to-market on the related derivatives	(62)		(115)
Net realized gain on the related long-term debt derivatives	16		16
Gain (loss) on instruments designated at fair value and related derivatives	(25)		(237)
Hybrid Instruments [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	(316)	[1]	(429)	[1]
Credit risk component	33		33
Total mark-to-market on financial instruments designated at fair value	(283)		(396)
Net realized loss on the financial instruments	0		0
Mark-to-market on the related derivatives	268		389
Net realized gain on the related long-term debt derivatives	0		0
Gain (loss) on instruments designated at fair value and related derivatives	$ (15)		$ (7)

[1] As it relates to hybrid instruments, interest rate and other components includes interest rate, foreign exchange and equity contract risks.