Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on the related derivatives		$ 340	$ 165
Gain (loss) on instruments designated at fair value and related derivatives		34	216
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]	(337)	(151)
Credit risk component, total	[2]	(1)	190
Total mark-to-market on financial instruments designated at fair value		(338)	39
Mark-to-market on the related derivatives		357	161
Net realized gain on the related long-term debt derivatives		15	16
Gain (loss) on instruments designated at fair value and related derivatives		34	216
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]	(1)	(3)
Total mark-to-market on financial instruments designated at fair value		(1)	(3)
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)	(3)
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]	6	5
Credit risk component, assets	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		6	5
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		6	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]	1	5
Credit risk component, assets	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		1	5
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	5
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]	19	(127)
Credit risk component, liabilities	[2]	0	149
Total mark-to-market on financial instruments designated at fair value		19	22
Mark-to-market on the related derivatives		(24)	127
Net realized gain on the related long-term debt derivatives		15	16
Gain (loss) on instruments designated at fair value and related derivatives		10	165
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]	(363)	(34)
Credit risk component, liabilities	[2]	0	44
Total mark-to-market on financial instruments designated at fair value		(363)	10
Mark-to-market on the related derivatives		381	34
Net realized gain on the related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ 18	$ 44

[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.