Credit Loss Reserves - Summarizes Changes in Credit Loss Reserves by Product/Class and Related Receivable Balance by Product (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016		Sep. 30, 2017	Sep. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Credit loss reserve balances at beginning of period			$ 254			$ 311
Provision for credit losses		$ 0	572	[1]	$ 0	621	[1]
Net charge-offs:
Charge-offs	[1],[2]		(827)			(938)
Recoveries			1			6
Total net charge-offs			(826)			(932)
Credit loss reserve balance at end of period			0			0
Initial lower of amortized cost or fair value adjustment			562			587
Real Estate Secured Receivable Portfolio [Member]
Net charge-offs:
Charge-offs			(244)			(268)
First lien [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Credit loss reserve balances at beginning of period			102			137
Provision for credit losses	[1]		75			107
Net charge-offs:
Charge-offs	[1],[2]		(178)			(247)
Recoveries			1			3
Total net charge-offs			(177)			(244)
Credit loss reserve balance at end of period			0			0
Second lien [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Credit loss reserve balances at beginning of period			152			174
Provision for credit losses	[1]		497			514
Net charge-offs:
Charge-offs	[1],[2]		(649)			(691)
Recoveries			0			3
Total net charge-offs			(649)			(688)
Credit loss reserve balance at end of period			0			0
Provision for Loan and Lease Losses [Member]
Net charge-offs:
Initial lower of amortized cost or fair value adjustment	[3]		$ 557			$ 576

[1] 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.

[2] 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.

[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).