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, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	$ (374)	$ (1)	$ (768)	$ (330)
Credit risk component	(204)	375	(283)	436
Total mark-to-market on financial instruments designated at fair value	(578)	374	(1,051)	106
Net realized gains on the financial instrument	1	(3)		(1)
Mark-to-market on the related derivatives	375	(9)	747	286
Net realized gain (losses) on the related derivatives	15	17	46	49
Gain (loss) on instruments designated at fair value and related derivatives	(187)	379	(258)	440
Loans [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	1	(5)	2	(7)
Credit risk component	14	(41)	48	(25)
Total mark-to-market on financial instruments designated at fair value	15	(46)	50	(32)
Net realized gains on the financial instrument	1	(3)		(1)
Mark-to-market on the related derivatives		1
Gain (loss) on instruments designated at fair value and related derivatives	16	(48)	50	(33)
Long-term Debt [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	14	(296)	(26)	(312)
Credit risk component	(179)	368	(269)	375
Total mark-to-market on financial instruments designated at fair value	(165)	72	(295)	63
Mark-to-market on the related derivatives	(21)	328	6	344
Net realized gain (losses) on the related derivatives	15	17	46	49
Gain (loss) on instruments designated at fair value and related derivatives	(171)	417	(243)	456
Hybrid Instruments [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate component	(389)	300	(744)	(11)
Credit risk component	(39)	48	(62)	86
Total mark-to-market on financial instruments designated at fair value	(428)	348	(806)	75
Mark-to-market on the related derivatives	396	(338)	741	(58)
Gain (loss) on instruments designated at fair value and related derivatives	$ (32)	$ 10	$ (65)	$ 17