Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on the related derivatives		$ 165	$ 388
Gain (loss) on instruments designated at fair value and related derivatives		216	85
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	[1]	(151)	(370)
Credit risk component, total	[2],[3]	190	89
Total mark-to-market on financial instruments designated at fair value		39	(281)
Mark-to-market on the related derivatives		161	349
Net realized gain on the related long-term debt derivatives		16	17
Gain (loss) on instruments designated at fair value and related derivatives		216	85
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Loans [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	[1]	0	0
Credit risk component, assets	[2],[3]	(3)	(10)
Total mark-to-market on financial instruments designated at fair value		(3)	(10)
Mark-to-market on the related derivatives		0	0
Net realized gain on the related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		(3)	(10)
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Securities purchased under resale agreements [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	[1]	5	0
Credit risk component, assets	[2],[3]	0	0
Total mark-to-market on financial instruments designated at fair value		5	0
Mark-to-market on the related derivatives		0	0
Net realized gain on the related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		5	0
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Securities sold under repurchase agreements [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	[1]	5	0
Credit risk component, assets	[2],[3]	0	0
Total mark-to-market on financial instruments designated at fair value		5	0
Mark-to-market on the related derivatives		0	0
Net realized gain on the related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		5	0
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Long-term debt [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	[1]	(127)	(82)
Credit risk component, liabilities	[2],[3]	149	70
Total mark-to-market on financial instruments designated at fair value		22	(12)
Mark-to-market on the related derivatives		127	70
Net realized gain on the related long-term debt derivatives		16	17
Gain (loss) on instruments designated at fair value and related derivatives		165	75
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Hybrid Instrument [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	[1]	(34)	(288)
Credit risk component, liabilities	[2],[3]	44	29
Total mark-to-market on financial instruments designated at fair value		10	(259)
Mark-to-market on the related derivatives		34	279
Net realized gain on the related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ 44	$ 20

[1] As it relates to hybrid instruments, interest rate and other components includes interest rate, foreign exchange and equity contract risks.

[2] During the first quarter of 2016 and 2015, the gains in the credit risk component for long-term debt were attributable to the widening of our own credit spreads

[3] During the first quarter of 2016, the gain in the credit risk component for hybrid instruments was attributable primarily to the widening of our own credit spreads related to structured notes, partially offset by the tightening of credit spreads on structured deposits while the gain during the first quarter of 2015 was attributable primarily to the widening of our own credit spreads related to structured notes.