Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on the related derivatives		$ 227	$ 171	$ 567	$ 336
Gain (loss) on instruments designated at fair value and related derivatives		(1)	(38)	33	178
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]	(227)	(202)	(564)	(353)
Credit risk component, total	[2]	(1)	(36)	(2)	154
Total mark-to-market on financial instruments designated at fair value		(228)	(238)	(566)	(199)
Mark-to-market on the related derivatives		213	184	570	345
Net realized gain on the related long-term debt derivatives		14	16	29	32
Gain (loss) on instruments designated at fair value and related derivatives		(1)	(38)	33	178
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	0	0
Credit risk component, assets	[2]	(1)	3	(2)	0
Total mark-to-market on financial instruments designated at fair value		(1)	3	(2)	0
Mark-to-market on the related derivatives		0	0	0	0
Net realized gain on the related long-term debt derivatives		0	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		(1)	3	(2)	0
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]	1	0	7	5
Credit risk component, assets	[2]	0	0	0	0
Total mark-to-market on financial instruments designated at fair value		1	0	7	5
Mark-to-market on the related derivatives		0	0	0	0
Net realized gain on the related long-term debt derivatives		0	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		1	0	7	5
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]	2	(4)	3	1
Credit risk component, assets	[2]	0	0	0	0
Total mark-to-market on financial instruments designated at fair value		2	(4)	3	1
Mark-to-market on the related derivatives		0	0	0	0
Net realized gain on the related long-term debt derivatives		0	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		2	(4)	3	1
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]	(26)	(70)	(7)	(197)
Credit risk component, liabilities	[2]	0	(41)	0	108
Total mark-to-market on financial instruments designated at fair value		(26)	(111)	(7)	(89)
Mark-to-market on the related derivatives		17	67	(7)	194
Net realized gain on the related long-term debt derivatives		14	16	29	32
Gain (loss) on instruments designated at fair value and related derivatives		5	(28)	15	137
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]	(204)	(128)	(567)	(162)
Credit risk component, liabilities	[2]	0	2	0	46
Total mark-to-market on financial instruments designated at fair value		(204)	(126)	(567)	(116)
Mark-to-market on the related derivatives		196	117	577	151
Net realized gain on the related long-term debt derivatives		0	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ (8)	$ (9)	$ 10	$ 35

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

[2] As discussed more fully in Note 19, "New Accounting Pronouncements," beginning January 1, 2017, the fair value movement on fair value option liabilities attributable to credit spread is recorded in common equity as a component of other comprehensive income.