Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on the related derivatives		$ 414	$ 9	$ 944
Gain (loss) on instruments designated at fair value and related derivatives		(71)	264	75
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]	(541)	98	(920)
Credit risk component, total	[2],[3]	(14)	200	82
Total mark-to-market on financial instruments designated at fair value		(555)	298	(838)
Mark-to-market on the related derivatives		421	(102)	845
Net realized gain on the related long-term debt derivatives		63	68	68
Gain (loss) on instruments designated at fair value and related derivatives		(71)	264	75
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],[3]	22	(14)	0
Total mark-to-market on financial instruments designated at fair value		22	(14)	0
Mark-to-market on the related derivatives		0	0	0
Net realized gain on the related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		22	(14)	0
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	0	0
Credit risk component, assets	[2],[3]	0	0	0
Total mark-to-market on financial instruments designated at fair value		0	0	0
Mark-to-market on the related derivatives		0	0	0
Net realized gain on the related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		0	0	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]	4	(6)	0
Credit risk component, assets	[2],[3]	0	0	0
Total mark-to-market on financial instruments designated at fair value		4	(6)	0
Mark-to-market on the related derivatives		0	0	0
Net realized gain on the related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		4	(6)	0
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]	(2)	(23)	(292)
Credit risk component, liabilities	[2],[3]	(3)	194	6
Total mark-to-market on financial instruments designated at fair value		(5)	171	(286)
Mark-to-market on the related derivatives		(31)	7	239
Net realized gain on the related long-term debt derivatives		63	68	68
Gain (loss) on instruments designated at fair value and related derivatives		27	246	21
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]	(543)	127	(628)
Credit risk component, liabilities	[2],[3]	(33)	20	76
Total mark-to-market on financial instruments designated at fair value		(576)	147	(552)
Mark-to-market on the related derivatives		452	(109)	606
Net realized gain on the related long-term debt derivatives		0	0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ (124)	$ 38	$ 54

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

[2] During 2016, the loss in the credit risk component for hybrid instruments was attributable to the tightening of credit spreads on structured deposits, partially offset by the widening of our own credits spreads related to structured notes. During 2015, the gain in the credit risk component for hybrid instruments was attributable primarily to the widening of credit spreads on structured deposits, partially offset by a loss due to changes in estimates associated with the valuation techniques used to measure the fair value of certain structured notes and deposits.

[3] During 2016, the loss in the credit risk component for long term debt was attributable to the tightening of our own credit spreads while the gains during 2015 and 2014 were attributable to the widening of our own credit spreads.