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Held-for-sale Operations - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Provision for credit losses	$ 507	$ 449
Goodwill impairment			$ 149
Corporate and Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill impairment			149
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations \| Ally Lending
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Provision for credit losses			16
Net pretax loss			133
Additional pretax loss	$ 7
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations \| Ally Lending \| Corporate and Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill impairment			$ 149