Fair Value Measurements - Changes in Level 3 Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012 Interest rate [Member]	Sep. 30, 2011 Interest rate [Member]	Sep. 30, 2012 Interest rate [Member]	Sep. 30, 2011 Interest rate [Member]	Sep. 30, 2012 Energy and commodity [Member]	Sep. 30, 2011 Energy and commodity [Member]	Jun. 30, 2012 Energy and commodity [Member]	Sep. 30, 2012 Credit [Member]	Sep. 30, 2011 Credit [Member]	Sep. 30, 2012 Credit [Member]	Sep. 30, 2011 Credit [Member]	Sep. 30, 2011 Trading Account Assets [Member] Other mortgage-backed securities [Member]	Sep. 30, 2012 Trading Account Assets [Member] Other mortgage-backed securities [Member]	Sep. 30, 2011 Trading Account Assets [Member] Other mortgage-backed securities [Member]	Jun. 30, 2012 Trading Account Assets [Member] Other mortgage-backed securities [Member]	Sep. 30, 2012 Trading Account Assets [Member] Other securities [Member]	Sep. 30, 2011 Trading Account Assets [Member] Other securities [Member]	Sep. 30, 2012 Trading Account Assets [Member] Other securities [Member]	Sep. 30, 2011 Trading Account Assets [Member] Other securities [Member]	Sep. 30, 2012 Other Investments [Member] Principal direct investments [Member]	Sep. 30, 2011 Other Investments [Member] Principal direct investments [Member]	Sep. 30, 2012 Other Investments [Member] Principal direct investments [Member]	Sep. 30, 2011 Other Investments [Member] Principal direct investments [Member]	Sep. 30, 2012 Other Investments [Member] Principal indirect investments [Member]	Sep. 30, 2011 Other Investments [Member] Principal indirect investments [Member]	Sep. 30, 2012 Other Investments [Member] Principal indirect investments [Member]	Sep. 30, 2011 Other Investments [Member] Principal indirect investments [Member]	Sep. 30, 2012 Other Investments [Member] Equity and Mezzanine Direct Investments [Member]	Sep. 30, 2011 Other Investments [Member] Equity and Mezzanine Direct Investments [Member]	Sep. 30, 2012 Other Investments [Member] Equity and Mezzanine Direct Investments [Member]	Sep. 30, 2011 Other Investments [Member] Equity and Mezzanine Direct Investments [Member]	Sep. 30, 2012 Other Investments [Member] Equity And Mezzanine Indirect Investments [Member]	Sep. 30, 2011 Other Investments [Member] Equity And Mezzanine Indirect Investments [Member]	Sep. 30, 2012 Other Investments [Member] Equity And Mezzanine Indirect Investments [Member]	Sep. 30, 2011 Other Investments [Member] Equity And Mezzanine Indirect Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 35	$ 81	$ 38	$ 75	$ (1)	$ 1	$ (1)	$ 5	$ 8	$ (21)	$ 11	$ 1	$ 35	$ 1	$ 1	$ 57			$ 21	$ 231	$ 270	$ 225	$ 372	$ 482	$ 470	$ 473	$ 526	$ 18	$ 14	$ 15	$ 20	$ 43	$ 33	$ 36	$ 30
Gains (losses) included in earnings	(2)	40	(5)	54	1	(1)			(1)	(11)	(11)		2			4	(1)	2	2	4	2	12	4	7	33	50	76		4	3	17			6
Purchases			1	11	(1)															1	8	11	38	4	10	24	56						3	4	12
Sales	(6)	(4)	(7)	(24)					(1)		(1)		(32)							(22)	(15)	(34)	(24)	(38)	(19)	(92)	(55)
Issuances
Settlements								4	1	37	8					(5)	1	(3)	(23)									(18)	(5)	(18)	(24)			(4)	(3)
Transfers into Level 3	3	1	7	11								33		33				57														(1)
Transfers out of Level 3	(7)	(4)	(11)	(13)									(4)										(125)				(109)								(3)
Ending Balance	23	114	23	114	(1)		(1)	5	7	5	7	34	1	34	1	56		56		214	265	214	265	455	494	455	494		13		13	42	36	42	36
Unrealized gains (losses) included in earnings																$ 4	$ (1)	$ 2	$ 2	$ 2	$ (3)	$ 10	$ 5	$ (7)	$ 27	$ 21	$ 55	$ 5	$ 4	$ 15	$ 36			$ 6	$ (3)