Fair Value Measurement- Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2015		Dec. 31, 2014
Fair value measurements for assets using significant unobservable inputs
Transfers out of Level 3	$ (1)
Included in earnings (or changes in net assets)	0
Derivative assets
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			(1)	[1]
Other Assets
Fair value measurements for assets using significant unobservable inputs
Beginning balance	105		70
Included in earnings (or changes in net assets)	2	[2]	(2)	[2]
Purchases	8		7
Sales	(5)		(21)
Ending balance	110		54
Total Assets
Fair value measurements for assets using significant unobservable inputs
Beginning balance	139		90
Included in earnings (or changes in net assets)			(3)
Purchases	8		7
Sales	(5)		(21)
Settlements			(2)
Ending balance	141		71
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	(2)		(1)
Total liabilities
Fair value measurements for liabilities using significant unobservable inputs
Beginning balance	75		9
Transfers out of Level 3	(37)
Included in earnings (or changes in net liabilities)	3		(1)
Settlements			(2)
Ending balance	41		6
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	3		1
Securities available-for-sale | State and political subdivisions
Fair value measurements for assets using significant unobservable inputs
Beginning balance	11				11
Included in earnings (or changes in net assets)	0	[3]
Ending balance	11		11		11
Trading Assets | Debt and equity instruments
Fair value measurements for assets using significant unobservable inputs
Beginning balance	1
Included in earnings (or changes in net assets)	0	[4]
Sales	0
Ending balance	1
Trading Assets | Derivative assets
Fair value measurements for assets using significant unobservable inputs
Beginning balance	22	[1]	9	[1]
Transfers out of Level 3	(1)	[1]
Included in earnings (or changes in net assets)	(2)	[1],[4]	(1)	[1],[4]
Settlements			(2)	[1]
Ending balance	19	[1]	6	[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	(2)	[1]
Trading Liabilities | Derivative liabilities
Fair value measurements for liabilities using significant unobservable inputs
Beginning balance	75	[5]	9	[5]
Transfers out of Level 3	(37)	[5]
Included in earnings (or changes in net liabilities)	3	[4],[5]	(1)	[4],[5]
Settlements			(2)	[5]
Ending balance	41	[5]	6	[5]
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	$ 3	[5]	$ 1	[5]

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

[2] Reported in investment and other income.

[3] 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).

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

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