Fair Value Measurement and Fair Value of Financial Instruments - Reconciliation of Assets and Liabilities Measured at fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) (Fair Value Measurements Recurring [Member], 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
	Sep. 30, 2012 Trading Liabilities [Member]	Sep. 30, 2011 Trading Liabilities [Member]	Sep. 30, 2012 Trading Liabilities [Member]	Sep. 30, 2011 Trading Liabilities [Member]	Sep. 30, 2012 Other Liabilities [Member]	Sep. 30, 2011 Other Liabilities [Member]	Sep. 30, 2012 Other Liabilities [Member]	Sep. 30, 2011 Other Liabilities [Member]	Sep. 30, 2012 Securities Available-for-Sale [Member]	Sep. 30, 2012 Securities Available-for-Sale [Member]	Sep. 30, 2011 Securities Available-for-Sale [Member]	Jun. 30, 2011 Securities Available-for-Sale [Member]	Sep. 30, 2012 Trading account assets [Member]	Sep. 30, 2012 Trading account assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, beginning of period									$ 1,134	$ 48	$ 8	$ 48	$ 118
Reconciliation of liability balance at fair value on a recurring basis using significant unobservable inputs, beginning of period	(118)	(8)		(14)	(72)	(41)	(51)	(36)
Total gains (losses) (realized/unrealized):
Included in income before taxes	(37)	(1)	(3)	5	(5)	(4)	(26)	(9)					37	3
Included in other comprehensive income									(43)	(47)	(1)
Purchases/additions, assets									383	1,473	42		3	5
Purchases/additions, liability	(3)		(5)
Sales	3		6								(1)		(3)	(6)
Settlements									(48)	(48)
Transfers into Level 3, assets														153
Transfers into Level 3, liability			(153)
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, end of period									1,426	1,426			155	155
Reconciliation of liability balance at fair value on a recurring basis using significant unobservable inputs, ending of period	(155)	(9)	(155)	(9)	(77)	(45)	(77)	(45)
Reconciliation of asset balance at fair value on a recurring basis using significant unobservable inputs, end of period									1,426	1,426	48	48	155	155
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	$ (37)	$ (1)	$ (3)	$ 5	$ (5)	$ (4)	$ (26)	$ (9)					$ 37	$ 3