Debt - Repayments of Principal and Interest (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total Debt	$ 88,938	$ 90,988
Interest payments in 2020	2,485
Interest payments in 2021	1,573
Interest payments in 2022	982
Interest payments in 2023	707
Interest payments in 2024	431
Interest payments thereafter	477
Interest payments	6,655
Total repayments in 2020	38,072
Total repayments in 2021	22,263
Total repayments in 2022	12,745
Total repayments in 2023	7,745
Total repayments in 2024	6,226
Total repayments thereafter	8,637
Total repayments of principal and interest	95,688
Secured Debt [Member]
Debt Instrument [Line Items]
Repayments of principal in 2020	24,089
Repayments of principal in 2021	10,233
Repayments of principal in 2022	3,781
Repayments of principal in 2023	1,182
Repayments of principal in 2024	731
Repayments of principal thereafter	0
Total Debt	40,016
Unsecured Debt [Member]
Debt Instrument [Line Items]
Repayments of principal in 2020	11,498
Repayments of principal in 2021	10,457
Repayments of principal in 2022	7,982
Repayments of principal in 2023	5,856
Repayments of principal in 2024	5,064
Repayments of principal thereafter	8,160
Total Debt	$ 49,017

Amount of interest payments scheduled after the fifth fiscal year following the latest fiscal year.

No definition available.

Name:	acf_DebtMaturitiesRepaymentsOfInterestAfterYearFive
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest payments scheduled in the next fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfInterestInNextTwelveMonths
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest payments scheduled in the fifth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfInterestInYearFive
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest payments scheduled in the fourth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfInterestInYearFour
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest payments scheduled in the third fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfInterestInYearThree
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest payments scheduled in the second fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfInterestInYearTwo
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of principal and interest payments scheduled after the fifth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfPrincipalAndInterestAfterYearFive
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of principal and interest payments scheduled in the next fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfPrincipalAndInterestInNextTwelveMonths
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of principal and interest payments scheduled in the fifth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFive
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of principal and interest payments scheduled in the fourth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFour
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of principal and interest payments scheduled in the third fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfPrincipalAndInterestInYearThree
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of principal and interest payments scheduled in the second fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	acf_DebtMaturitiesRepaymentsOfPrincipalAndInterestInYearTwo
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Repayments of Principal and Interest

+ References

No definition available.

+ Details

Name:	acf_RepaymentsofPrincipalandInterest
Namespace Prefix:	acf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount of interest payable on debt, including, but not limited to, trade payables.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: