Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives		$ (1,131)	$ 1,136	$ 414
Gain (loss) on instruments designated at fair value and related derivatives		19	43	(71)
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]	1,135	(1,144)	(541)
Credit risk component, total	[2]	(4)	(2)	(14)
Total mark-to-market on financial instruments designated at fair value		1,131	(1,146)	(555)
Mark-to-market on related derivatives		(1,157)	1,132	421
Net realized gain on related long-term debt derivatives		45	57	63
Gain (loss) on instruments designated at fair value and related derivatives		19	43	(71)
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
Credit risk component, assets	[2]	(4)	(2)	22
Total mark-to-market on financial instruments designated at fair value		(4)	(2)	22
Mark-to-market on related derivatives		0	0	0
Net realized gain on related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		(4)	(2)	22
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]	0	(1)	0
Credit risk component, assets	[2]	0	0	0
Total mark-to-market on financial instruments designated at fair value		0	(1)	0
Mark-to-market on related derivatives		0	0	0
Net realized gain on related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		0	(1)	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]	1	2	4
Credit risk component, liabilities	[2]	0	0	0
Total mark-to-market on financial instruments designated at fair value		1	2	4
Mark-to-market on related derivatives		0	0	0
Net realized gain on related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		1	2	4
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]	99	6	(2)
Credit risk component, liabilities	[2]	0	0	(3)
Total mark-to-market on financial instruments designated at fair value		99	6	(5)
Mark-to-market on related derivatives		(95)	(31)	(31)
Net realized gain on related long-term debt derivatives		45	57	63
Gain (loss) on instruments designated at fair value and related derivatives		49	32	27
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]	1,035	(1,151)	(543)
Credit risk component, liabilities	[2]	0	0	(33)
Total mark-to-market on financial instruments designated at fair value		1,035	(1,151)	(576)
Mark-to-market on related derivatives		(1,062)	1,163	452
Net realized gain on related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ (27)	$ 12	$ (124)

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

[2] he 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).