Fair Value Option - Components of Gain on Instruments at Fair Value and Related Derivatives (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	$ (240)	[1]	$ (374)	[1]	$ (169)	[1]	$ (768)	[1]
Credit risk component	(24)		(204)		95		(283)
Total mark-to-market on financial instruments designated at fair value	(264)		(578)		(74)		(1,051)
Net realized loss on the financial instruments			1		(8)
Mark-to-market on the related derivatives	241		375		115		747
Net realized gain on the related long-term debt derivatives	17		15		49		46
Gain (loss) on instruments designated at fair value and related derivatives	(6)		(187)		82		(258)
Loans [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	0	[1]	1	[1]	0	[1]	2	[1]
Credit risk component	0		14		21		48
Total mark-to-market on financial instruments designated at fair value	0		15		21		50
Net realized loss on the financial instruments			1		(8)
Mark-to-market on the related derivatives	0		0		0		0
Net realized gain on the related long-term debt derivatives	0		0		0		0
Gain (loss) on instruments designated at fair value and related derivatives	0		16		13		50
Long-term Debt [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	40	[1]	14	[1]	223	[1]	(26)	[1]
Credit risk component	(63)		(179)		(52)		(269)
Total mark-to-market on financial instruments designated at fair value	(23)		(165)		171		(295)
Net realized loss on the financial instruments			0		0
Mark-to-market on the related derivatives	(39)		(21)		(229)		6
Net realized gain on the related long-term debt derivatives	17		15		49		46
Gain (loss) on instruments designated at fair value and related derivatives	(45)		(171)		(9)		(243)
Hybrid Instruments [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(280)	[1]	(389)	[1]	(392)	[1]	(744)	[1]
Credit risk component	39		(39)		126		(62)
Total mark-to-market on financial instruments designated at fair value	(241)		(428)		(266)		(806)
Net realized loss on the financial instruments			0		0
Mark-to-market on the related derivatives	280		396		344		741
Net realized gain on the related long-term debt derivatives	0		0		0		0
Gain (loss) on instruments designated at fair value and related derivatives	$ 39		$ (32)		$ 78		$ (65)

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