Fair Value Option - Components of Gain (Loss) on Debt Designated at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Mark-to-market on debt designated at fair value :
Interest rate component	[1]	$ 8	$ 24	$ 34	$ 42
Credit risk component(2)	[1],[2]	0	(27)	0	(8)
Total mark-to-market on debt designated at fair value	[1]	8	(3)	34	34
Mark-to-market on the related derivatives	[1],[3]	(1)	(16)	(27)	(40)
Net realized gains on the related derivatives	[1]	1	11	17	38
Gain (loss) on debt designated at fair value and related derivatives		8	(8)	24	32
Fair value option debt attributable to credit spread, before tax (less than $1 million for the 3 months ended June 30, 2017)		(5)		(13)
Foreign currency translation gains (losses) recorded in derivatives		(4)	(22)	(76)	(68)
Offsetting gains (losses) recorded in derivative related income (expense)		$ 4	$ 22	$ 76	$ 68

[1] The derivatives associated with debt designated at fair value are economic hedges but do not qualify for hedge accounting. See Note 6, "Derivative Financial Instruments," for additional discussion of these non-qualifying hedges.

[2] As discussed below and more fully in Note 13, "New Accounting Pronouncements," beginning January 1, 2017, the fair value movement on fair value option debt attributable to our own credit spread is recorded in common equity as a component of other comprehensive income (loss). For the three and nine months ended September 30, 2017, the fair value movement on fair value option debt attributable to our own credit spread was a loss of $5 million and loss of $13 million, respectively.

[3] Mark-to-market on debt designated at fair value and related derivatives excludes market value changes due to fluctuations in foreign currency exchange rates. Foreign currency translation gains (losses) recorded in derivative related income (expense) associated with debt designated at fair value was a loss of $4 million and a loss of $22 million for the three months ended September 30, 2017 and 2016, respectively, and a loss of $76 million and a loss of $68 million for the nine months ended September 30, 2017 and 2016, respectively. Offsetting gains (losses) recorded in derivative related income (expense) associated with the related derivatives was a gain of $4 million and a gain of $22 million for the three months ended September 30, 2017 and 2016, respectively, and a gain of $76 million and a gain of $68 million for the nine months ended September 30, 2017 and 2016, respectively.