Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	$ 1,242	$ 1,276
Allowance for loan and lease losses, charge-offs	(360)	(377)
Allowance for loan and lease losses, recoveries	123	118
Allowance for loan and lease losses, net charge-offs	(237)	(259)
Provision for loan losses	282	261
Allowance for loan losses	1,288	1,278
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	126	88
Allowance for loan losses, collectively evaluated for impairment	1,162	1,190
Finance receivables and loans, net	130,055	125,327	$ 129,926
Finance receivables and loans, individually evaluated for impairment	997	840
Finance receivables and loans, collectively evaluated for impairment	129,058	124,487
Allowance for Loan and Lease Losses, Adjustments, Other	1
Consumer portfolio segment \| Automobile loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	1,048	1,066
Allowance for loan and lease losses, charge-offs	(352)	(365)
Allowance for loan and lease losses, recoveries	118	112
Allowance for loan and lease losses, net charge-offs	(234)	(253)
Provision for loan losses	257	253
Allowance for loan losses	1,070	1,066
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	46	40
Allowance for loan losses, collectively evaluated for impairment	1,024	1,026
Finance receivables and loans, net	71,553	69,318	70,539
Finance receivables and loans, individually evaluated for impairment	501	463
Finance receivables and loans, collectively evaluated for impairment	71,052	68,855
Allowance for Loan and Lease Losses, Adjustments, Other	(1)
Consumer portfolio segment \| Residential mortgage
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	53	79
Allowance for loan and lease losses, charge-offs	(3)	(12)
Allowance for loan and lease losses, recoveries	5	6
Allowance for loan and lease losses, net charge-offs	2	(6)
Provision for loan losses	(3)	1
Allowance for loan losses	52	74
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	22	27
Allowance for loan losses, collectively evaluated for impairment	30	47
Finance receivables and loans, net	17,658	14,683	16,701
Finance receivables and loans, individually evaluated for impairment	227	230
Finance receivables and loans, collectively evaluated for impairment	17,431	14,453
Allowance for Loan and Lease Losses, Adjustments, Other	0
Commercial portfolio segment \| Commercial loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	141	131
Allowance for loan and lease losses, charge-offs	(5)	0
Allowance for loan and lease losses, recoveries	0	0
Allowance for loan and lease losses, net charge-offs	(5)	0
Provision for loan losses	28	7
Allowance for loan losses	166	138
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	58	21
Allowance for loan losses, collectively evaluated for impairment	108	117
Finance receivables and loans, net	40,844	41,326	$ 42,686
Finance receivables and loans, individually evaluated for impairment	269	147
Finance receivables and loans, collectively evaluated for impairment	40,575	$ 41,179
Allowance for Loan and Lease Losses, Adjustments, Other	$ 2

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

Name:	us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesAdjustmentsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossAdditionalInformationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of expense related to loss from loan transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

+ Details

Name:	us-gaap_ProvisionForLoanLossesExpensed
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_AutomobileLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: