Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on the related derivatives		$ 350	$ 171	$ 917	$ 507
Gain (loss) on instruments designated at fair value and related derivatives		7	(88)	40	90
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]	(356)	(228)	(920)	(581)
Credit risk component, total	[2]	(1)	(54)	(3)	100
Total mark-to-market on financial instruments designated at fair value		(357)	(282)	(923)	(481)
Mark-to-market on the related derivatives		348	178	918	523
Net realized gain on the related long-term debt derivatives		16	16	45	48
Gain (loss) on instruments designated at fair value and related derivatives		7	(88)	40	90
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)	6	(3)	6
Total mark-to-market on financial instruments designated at fair value		(1)	6	(3)	6
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)	6	(3)	6
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)	(4)	6	1
Credit risk component, assets	[2]	0	0	0	0
Total mark-to-market on financial instruments designated at fair value		(1)	(4)	6	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		(1)	(4)	6	1
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]	0	1	3	2
Credit risk component, assets	[2]	0	0	0	0
Total mark-to-market on financial instruments designated at fair value		0	1	3	2
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		0	1	3	2
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]	0	(5)	(7)	(202)
Credit risk component, liabilities	[2]	0	5	0	113
Total mark-to-market on financial instruments designated at fair value		0	0	(7)	(89)
Mark-to-market on the related derivatives		(6)	(10)	(13)	184
Net realized gain on the related long-term debt derivatives		16	16	45	48
Gain (loss) on instruments designated at fair value and related derivatives		10	6	25	143
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]	(355)	(220)	(922)	(382)
Credit risk component, liabilities	[2]	0	(65)	0	(19)
Total mark-to-market on financial instruments designated at fair value		(355)	(285)	(922)	(401)
Mark-to-market on the related derivatives		354	188	931	339
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)	$ (97)	$ 9	$ (62)

[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 20, "New Accounting Pronouncements," beginning January 1, 2017, the fair value movement on fair value option liabilities attributable to our own credit spread is recorded in common equity as a component of other comprehensive income (loss).