Fair Value Measurement- Significant Unobservable Inputs (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
Fair value measurements for assets using significant unobservable inputs
Beginning Balance			$ 313				$ 365
Included in earnings (or changes in net assets)			(1)				(27)
Purchases			4				9
Sales			(26)				(46)
Settlements							(11)
Ending Balance			290				290
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period			(4)				(13)
Fair value measurements for liabilities using significant unobservable inputs
Beginning Balance	117		302		224		314
Transfers out of Level 3	(13)				(17)
Included in earnings (or changes in net liabilities)	(5)				(110)
Settlements	(7)		(2)		(5)		(14)
Ending Balance	92		300		92		300
Change in unrealized (gains) or losses for the period included in earnings (or changes in net assets) for liabilities held at the end of the reporting period	(1)		12		27		33
Debt and equity instruments
Fair value measurements for assets using significant unobservable inputs
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period					0
Derivative assets
Fair value measurements for assets using significant unobservable inputs
Ending Balance	26	[1]			26	[1]
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period					(13)	[2]
Other Assets
Fair value measurements for assets using significant unobservable inputs
Beginning Balance	113		138		120		157
Transfers out of Level 3	0				0
Included in earnings (or changes in net assets)	(2)	[3]	3	[3]	2	[4]	4	[4]
Purchases			3		3		8
Sales	(10)		(16)		(20)		(33)
Settlements							(8)
Ending Balance	101		128		101		128
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period	0				0		0
Total Assets
Fair value measurements for assets using significant unobservable inputs
Beginning Balance	209				271
Transfers out of Level 3	(14)				(19)
Included in earnings (or changes in net assets)	(4)				5
Purchases					3
Sales	(10)				(69)
Ending Balance	181				181
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period	0				(13)
Investment Management
Fair value measurements for assets using significant unobservable inputs
Beginning Balance					44
Transfers out of Level 3					0
Included in earnings (or changes in net assets)					(2)
Purchases					0
Sales					(46)
Ending Balance	0				0
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period					0
Available-for-sale | State and political subdivisions
Fair value measurements for assets using significant unobservable inputs
Beginning Balance	52		42		45		45
Transfers out of Level 3					0
Included in earnings (or changes in net assets)	(1)	[5]	2		(6)	[6]	2	[7]
Purchases					0
Sales					0
Settlements							(3)
Ending Balance	51		44		51		44
Available-for-sale | Other debt securities
Fair value measurements for assets using significant unobservable inputs
Beginning Balance							3
Included in earnings (or changes in net assets)							(3)	[7]
Purchases							0
Sales							0
Settlements							0
Ending Balance			0				0
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period							0
Trading Assets | Debt and equity instruments
Fair value measurements for assets using significant unobservable inputs
Beginning Balance	2		60		48		63
Transfers out of Level 3					0
Included in earnings (or changes in net assets)	1	[8]	0	[8]	(4)	[9]	0	[9]
Purchases			0		0		0
Sales	0		(10)		(49)		(13)
Settlements							0
Ending Balance	3		50		3		50
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period							0
Trading Assets | Derivative assets
Fair value measurements for assets using significant unobservable inputs
Beginning Balance	42	[1]	73	[1]	58	[2]	97	[2]
Transfers out of Level 3	(14)				(19)	[2]
Included in earnings (or changes in net assets)	(2)	[1],[8]	(6)	[1],[8]	13	[2],[9]	(30)	[2],[9]
Purchases			1	[1]	0	[2]	1	[2]
Sales			0	[1]	0	[2]	0	[2]
Settlements							0	[2]
Ending Balance	26	[2]	68	[1],[2]	26	[2]	68	[1],[2]
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period	0	[1]	(4)	[1]			(13)	[2]
Trading Liabilities | Derivative liabilities
Fair value measurements for liabilities using significant unobservable inputs
Beginning Balance	117	[10]	302	[8]	224	[11]	314	[11]
Transfers out of Level 3	(13)	[10]			(17)	[10]
Included in earnings (or changes in net liabilities)	(5)	[10],[8]			(110)	[10],[7]
Settlements	(7)		(2)	[7],[8]	(5)	[10]	(14)	[11],[7]
Ending Balance	92	[10],[11]	300	[11],[8]	92	[10],[11]	300	[11],[8]
Change in unrealized (gains) or losses for the period included in earnings (or changes in net assets) for liabilities held at the end of the reporting period	(1)	[10]	12	[8]	27	[11]	33	[11]
Investment Management
Fair value measurements for assets using significant unobservable inputs
Beginning Balance	44
Transfers out of Level 3	0
Included in earnings (or changes in net assets)	2
Sales	(46)
Ending Balance	0				0
Change in unrealized gains or (losses) for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period	$ 0

[1] Derivative assets are reported on a gross basis.

[2] (a)Derivative assets are reported on a gross basis.

[3] Reported in investment and other income.

[4] (d)Reported in investment and other income.

[5] Realized gains (losses) are reported in securities gains (losses). Unrealized gains (losses) are reported in accumulated other comprehensive income (loss) except for the credit portion of OTTI losses which are recorded in securities gains (losses).

[6] (b)Realized gains (losses) are reported in securities gains (losses). Unrealized gains (losses) are reported in accumulated other comprehensive income (loss) except for the credit portion of OTTI losses which are recorded in securities gains (losses).

[7] (b)Reported in foreign exchange and other trading revenue.

[8] Reported in foreign exchange and other trading revenue.

[9] (c)Reported in foreign exchange and other trading revenue.

[10] Derivative liabilities are reported on a gross basis.

[11] (a)Derivative liabilities are reported on a gross basis.