Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	$ 1,282	$ 1,257	$ 1,242	$ 1,276
Allowance for loan and lease losses, charge-offs	(393)	(353)	(1,071)	(1,036)
Allowance for loan and lease losses, recoveries	126	118	385	362
Allowance for loan and lease losses, net charge-offs	(267)	(235)	(686)	(674)
Provision for loan losses	263	233	722	652
Allowance for Loan and Lease Losses, Adjustments, Other	(1)	(7)	(1)	(6)
Allowance for loan losses	1,277	1,248	1,277	1,248
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	87	102	87	102
Allowance for loan losses, collectively evaluated for impairment	1,190	1,146	1,190	1,146
Finance receivables and loans, net	128,609	126,605	128,609	126,605	$ 129,926
Finance receivables and loans, individually evaluated for impairment	906	898	906	898
Finance receivables and loans, collectively evaluated for impairment	127,703	125,707	127,703	125,707
Consumer portfolio segment
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Finance receivables and loans, net	90,081		90,081		87,240
Consumer portfolio segment \| Automotive loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	1,078	1,053	1,048	1,066
Allowance for loan and lease losses, charge-offs	(374)	(343)	(1,027)	(1,004)
Allowance for loan and lease losses, recoveries	121	110	368	336
Allowance for loan and lease losses, net charge-offs	(253)	(233)	(659)	(668)
Provision for loan losses	264	229	701	650
Allowance for Loan and Lease Losses, Adjustments, Other	1	(6)	0	(5)
Allowance for loan losses	1,090	1,043	1,090	1,043
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	37	43	37	43
Allowance for loan losses, collectively evaluated for impairment	1,053	1,000	1,053	1,000
Finance receivables and loans, net	73,071	69,995	73,071	69,995	70,539
Finance receivables and loans, individually evaluated for impairment	514	483	514	483
Finance receivables and loans, collectively evaluated for impairment	72,557	69,512	72,557	69,512
Consumer portfolio segment \| Real estate-backed loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	49	66	53	79
Allowance for loan and lease losses, charge-offs	(3)	(7)	(11)	(27)
Allowance for loan and lease losses, recoveries	5	8	17	20
Allowance for loan and lease losses, net charge-offs	2	1	6	(7)
Provision for loan losses	(5)	(4)	(13)	(7)
Allowance for Loan and Lease Losses, Adjustments, Other	(2)	1	(2)	(1)
Allowance for loan losses	44	64	44	64
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	18	24	18	24
Allowance for loan losses, collectively evaluated for impairment	26	40	26	40
Finance receivables and loans, net	17,010	16,506	17,010	16,506	16,701
Finance receivables and loans, individually evaluated for impairment	213	231	213	231
Finance receivables and loans, collectively evaluated for impairment	16,797	16,275	16,797	16,275
Commercial portfolio segment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	155	138	141	131
Allowance for loan and lease losses, charge-offs	(16)	(3)	(33)	(5)
Allowance for loan and lease losses, recoveries	0	0	0	6
Allowance for loan and lease losses, net charge-offs	(16)	(3)	(33)	1
Provision for loan losses	4	8	34	9
Allowance for Loan and Lease Losses, Adjustments, Other	0	(2)	1	0
Allowance for loan losses	143	141	143	141
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	32	35	32	35
Allowance for loan losses, collectively evaluated for impairment	111	106	111	106
Finance receivables and loans, net	38,528	40,104	38,528	40,104	42,686
Finance receivables and loans, individually evaluated for impairment	179	184	179	184
Finance receivables and loans, collectively evaluated for impairment	38,349	$ 39,920	38,349	$ 39,920
Commercial portfolio segment \| Automotive loan
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Finance receivables and loans, net	29,122		29,122		33,672
Commercial portfolio segment \| Real estate-backed loan
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Finance receivables and loans, net	$ 5,029		$ 5,029		$ 4,809

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of other addition (reduction) in allowance reserve for credit loss.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount, after recoveries, of loans and leases that have been written-off.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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