Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on the related derivatives		$ (507)	$ 340
Gain (loss) on instruments designated at fair value and related derivatives		30	34
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]	529	(337)
Credit risk component, total	[2]	4	(1)
Total mark-to-market on financial instruments designated at fair value		533	(338)
Mark-to-market on the related derivatives		(516)	357
Net realized gain on the related long-term debt derivatives		13	15
Gain (loss) on instruments designated at fair value and related derivatives		30	34
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]	4	(1)
Total mark-to-market on financial instruments designated at fair value		4	(1)
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		4	(1)
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	6
Credit risk component, assets	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		0	6
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		0	6
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)	1
Credit risk component, liabilities	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		(1)	1
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		(1)	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]	88	19
Credit risk component, liabilities	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		88	19
Mark-to-market on the related derivatives		(77)	(24)
Net realized gain on the related long-term debt derivatives		13	15
Gain (loss) on instruments designated at fair value and related derivatives		24	10
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]	442	(363)
Credit risk component, liabilities	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		442	(363)
Mark-to-market on the related derivatives		(439)	381
Net realized gain on the related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ 3	$ 18

[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).