Guarantees and Commitments - Schedule of Financing Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Guarantor Obligations [Line Items]
Unused revolving credit line commitments and other	$ 10,027	$ 10,658
Commitments to provide capital to investees	1,227	1,191
Construction-lending commitments	166	168
Home equity lines of credit	116	134
Mortgage loan origination commitments	0	29
Unconditionally cancelable unfunded commitments	$ 16,500	18,700
Disposal Group, Held-for-Sale, Not Discontinued Operations \| Ally Lending
Guarantor Obligations [Line Items]
Unused revolving credit line commitments and other		$ 68

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

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