Fair Value Measurements - Change in Fair Values of Level 3 Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 38	$ 75
Gains (losses) included in earnings	(5)	53
Purchases	2	12
Sales	(7)	(44)
Issuances
Transfers into Level 3	8	13
Transfers out of Level 3	(17)	(71)
Ending Balance	19	38
Energy and Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	(1)	1
Gains (losses) included in earnings	1	(1)
Purchases	(1)	(1)
Issuances
Transfers into Level 3	2
Ending Balance	1	(1)
Credit [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	(21)	11
Gains (losses) included in earnings	(13)	(40)
Sales		(1)
Issuances
Settlements	38	9
Ending Balance	4	(21)
Trading Account Assets [Member] | Other Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	35	1
Gains (losses) included in earnings	1
Sales	(32)
Issuances
Transfers into Level 3		34
Transfers out of Level 3	(4)
Ending Balance		35
Trading Account Assets [Member] | Other securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		21
Gains (losses) included in earnings	3	2
Sales	(7)
Issuances
Settlements	(50)	(23)
Transfers into Level 3	57
Ending Balance	3
Unrealized gains (losses) included in earnings	4	2
Other Investments [Member] | Principal Investments Direct [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	225	372
Gains (losses) included in earnings	11	(2)
Purchases	12	39
Sales	(57)	(52)
Issuances
Transfers out of Level 3		(132)
Ending Balance	191	225
Unrealized gains (losses) included in earnings	14	11
Other Investments [Member] | Principal Investments Indirect [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	473	526
Gains (losses) included in earnings	52	70
Purchases	34	66
Sales	(123)	(80)
Issuances
Transfers out of Level 3		(109)
Ending Balance	436	473
Unrealized gains (losses) included in earnings	5	45
Other Investments [Member] | Equity And Mezzanine Investments Direct [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	15	20
Gains (losses) included in earnings	2	20
Issuances
Settlements	(17)	(25)
Ending Balance		15
Unrealized gains (losses) included in earnings	10	38
Other Investments [Member] | Equity And Mezzanine Investments Indirect [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	36	30
Gains (losses) included in earnings	8
Purchases	4	14
Issuances
Settlements	(7)	(5)
Transfers out of Level 3		(3)
Ending Balance	41	36
Unrealized gains (losses) included in earnings	$ 8	$ (3)