Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment		$ 89
Financing receivable, allowance for credit losses, collectively evaluated for impairment		1,174
Loans and leases receivable, gross	$ 118,534	128,231
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(1,263)	(1,242)
Allowance for loan and lease losses, charge-offs	(1,326)	(1,490)
Allowance for loan and lease losses, recoveries	562	514
Allowance for loan and lease losses, net charge-offs	(764)	(976)
Provision for credit losses	1,439	998
Other	(1)	(1)
Allowance for loan losses	(3,283)	(1,263)
Excludes fair value option elected other loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross		128,220
Financing receivable, individually evaluated for impairment		961
Financing receivable, collectively evaluated for impairment		127,259
Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(2,609)
Allowance for loan losses		(2,609)
Consumer portfolio segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross	89,202	89,924
Consumer portfolio segment \| Excludes fair value option elected other loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross	89,194	89,913
Consumer portfolio segment \| Automotive loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment		38
Financing receivable, allowance for credit losses, collectively evaluated for impairment		1,037
Loans and leases receivable, gross	73,668	72,390
Financing receivable, individually evaluated for impairment		538
Financing receivable, collectively evaluated for impairment		71,852
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(1,075)	(1,048)
Allowance for loan and lease losses, charge-offs	(1,244)	(1,423)
Allowance for loan and lease losses, recoveries	542	493
Allowance for loan and lease losses, net charge-offs	(702)	(930)
Provision for credit losses	1,194	957
Other	1	0
Allowance for loan losses	(2,902)	(1,075)
Consumer portfolio segment \| Automotive loan \| Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(2,409)
Allowance for loan losses		(2,409)
Consumer portfolio segment \| Real estate-backed loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment		18
Financing receivable, allowance for credit losses, collectively evaluated for impairment		28
Loans and leases receivable, gross	15,127	17,322
Financing receivable, individually evaluated for impairment		208
Financing receivable, collectively evaluated for impairment		17,114
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(46)	(53)
Allowance for loan and lease losses, charge-offs	(13)	(13)
Allowance for loan and lease losses, recoveries	16	21
Allowance for loan and lease losses, net charge-offs	3	8
Provision for credit losses	(10)	(13)
Other	0	(2)
Allowance for loan losses	(33)	(46)
Consumer portfolio segment \| Real estate-backed loan \| Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(40)
Allowance for loan losses		(40)
Consumer portfolio segment \| Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment		0
Financing receivable, allowance for credit losses, collectively evaluated for impairment		9
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(9)	0
Allowance for loan and lease losses, charge-offs	(15)	(5)
Allowance for loan and lease losses, recoveries	1	0
Allowance for loan and lease losses, net charge-offs	(14)	(5)
Provision for credit losses	62	14
Other	0	0
Allowance for loan losses	(73)	(9)
Consumer portfolio segment \| Other \| Excludes fair value option elected other loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross		201
Financing receivable, individually evaluated for impairment		0
Financing receivable, collectively evaluated for impairment		201
Consumer portfolio segment \| Other \| Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(25)
Allowance for loan losses		(25)
Commercial portfolio segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment		33
Financing receivable, allowance for credit losses, collectively evaluated for impairment		100
Loans and leases receivable, gross	29,332	38,307
Financing receivable, individually evaluated for impairment		215
Financing receivable, collectively evaluated for impairment		38,092
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(133)	(141)
Allowance for loan and lease losses, charge-offs	(54)	(49)
Allowance for loan and lease losses, recoveries	3	0
Allowance for loan and lease losses, net charge-offs	(51)	(49)
Provision for credit losses	193	40
Other	(2)	1
Allowance for loan losses	(275)	(133)
Commercial portfolio segment \| Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(135)
Allowance for loan losses		(135)
Commercial portfolio segment \| Automotive loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross	19,082	28,332
Commercial portfolio segment \| Real estate-backed loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross	5,008	4,961
Accounting Standards Update 2016-13 \| Retained Earnings \| Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(1,346)
Allowance for loan losses		(1,346)
Accounting Standards Update 2016-13 \| Retained Earnings \| Consumer portfolio segment \| Automotive loan \| Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(1,334)
Allowance for loan losses		(1,334)
Accounting Standards Update 2016-13 \| Retained Earnings \| Consumer portfolio segment \| Real estate-backed loan \| Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	6
Allowance for loan losses		6
Accounting Standards Update 2016-13 \| Retained Earnings \| Consumer portfolio segment \| Other \| Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(16)
Allowance for loan losses		(16)
Accounting Standards Update 2016-13 \| Retained Earnings \| Commercial portfolio segment \| Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	$ (2)
Allowance for loan losses		$ (2)

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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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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