Receivables Held for Sale - Additional Information (Detail) - USD ($)		3 Months Ended			9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Aggregate unpaid balance				$ 8,219,000,000			$ 8,577,000,000
Aggregate carrying value				8,087,000,000			8,429,000,000
Credit loss reserve	[1],[2]			827,000,000			938,000,000
Initial lower of amortized cost or fair value adjustment				562,000,000			587,000,000
Lower of amortized cost or fair value adjustment on loans held for sale		$ 16,000,000		565,000,000	$ (155,000,000)		695,000,000
Provision for Credit Losses [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Initial lower of amortized cost or fair value adjustment	[3]			557,000,000			576,000,000
Other Revenue [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Initial lower of amortized cost or fair value adjustment	[4]			5,000,000			11,000,000
Lower of amortized cost or fair value adjustment on loans held for sale		16,000,000	[5]	8,000,000	(155,000,000)	[5]	119,000,000
Subsequent to initial transfer to held for sale				3,000,000			108,000,000
Fair Value [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Lower of amortized cost or fair value adjustment on loans held for sale		10,000,000		577,000,000	(153,000,000)		732,000,000
Fair Value [Member] | Provision for Credit Losses [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Initial lower of amortized cost or fair value adjustment	[3]			557,000,000			576,000,000
Fair Value [Member] | Other Revenue [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Initial lower of amortized cost or fair value adjustment	[4]			5,000,000			11,000,000
Lower of amortized cost or fair value adjustment on loans held for sale		$ 10,000,000	[5]	20,000,000	$ (153,000,000)	[5]	156,000,000
Subsequent to initial transfer to held for sale				15,000,000			145,000,000
Real Estate Secured Receivable Portfolio [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Credit loss reserve				$ 244,000,000			$ 268,000,000

[1] For collateral dependent receivables that were transferred to held for sale, existing credit loss reserves at the time of transfer were recognized as a charge-off. We transferred to held for sale certain real estate secured receivables during the three and nine months ended September 30, 2016 and, accordingly, we recognized the existing credit loss reserves on these receivables as additional charge-off totaling $244 million and $268 million, respectively.

[2] The provision for credit losses and charge-offs for real estate secured receivables during the three and nine months ended September 30, 2016 included $557 million and $576 million, respectively, related to the initial lower of amortized cost or fair value adjustment attributable to credit factors for receivables transferred to held for sale. See Note 2, "Receivables Held for Sale," for additional information.

[3] Represents the portion of the initial lower of amortized cost or fair value adjustment attributable to credit factors which are recorded as provision for credit losses in the consolidated statement of income (loss).

[4] Represents the portion of the initial lower of amortized cost or fair value adjustment attributable to non-credit factors which are recorded as a component of total other revenues in the consolidated statement income (loss) as it reflects the impact on value caused by current marketplace conditions including changes in interest rates.

[5] As all of our receivables are classified as held for sale at September 30, 2017 and December 31, 2016, for the three and nine months ended September 30, 2017 and for all future periods, any lower of amortized cost or fair value adjustments will relate to either changes in fair value subsequent to classification as held for sale or settlements of receivables as discussed above.