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, 2019	Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives	$ 189	$ 193	$ 1,738		$ (209)
Gain (loss) on instruments designated at fair value and related derivatives	(19)	29	(45)		63
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	(213)	(178)	(1,816)	[1]	251	[1]
Credit risk component, total	(1)	0	2	[2]	3	[2]
Total mark-to-market on financial instruments designated at fair value	(214)	(178)	(1,814)		254
Mark-to-market on related derivatives	184	197	1,739		(225)
Net realized gain on related long-term debt derivatives	11	10	30		34
Gain (loss) on instruments designated at fair value and related derivatives	(19)	29	(45)		63
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	0	0	0	[1]	0	[1]
Credit risk component, assets	(1)	0	2	[2]	3	[2]
Total mark-to-market on financial instruments designated at fair value	(1)	0	2		3
Mark-to-market on related derivatives	0	0	0		0
Net realized gain on related long-term debt derivatives	0	0	0		0
Gain (loss) on instruments designated at fair value and related derivatives	(1)	0	2		3
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	(115)	51	(284)	[1]	173	[1]
Credit risk component, liabilities	0	0	0	[2]	0	[2]
Total mark-to-market on financial instruments designated at fair value	(115)	51	(284)		173
Mark-to-market on related derivatives	89	(44)	225		(154)
Net realized gain on related long-term debt derivatives	11	10	30		34
Gain (loss) on instruments designated at fair value and related derivatives	(15)	17	(29)		53
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	(98)	(229)	(1,532)	[1]	78	[1]
Credit risk component, liabilities	0	0	0	[2]	0	[2]
Total mark-to-market on financial instruments designated at fair value	(98)	(229)	(1,532)		78
Mark-to-market on related derivatives	95	241	1,514		(71)
Net realized gain on related long-term debt derivatives	0	0	0		0
Gain (loss) on instruments designated at fair value and related derivatives	$ (3)	$ 12	$ (18)		$ 7

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

[2] The fair value movement on fair value option liabilities attributable to our own credit spread is recorded in other comprehensive income (loss).