Held-for-sale Operations - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2024
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Provision for credit losses	$ (191)		$ (507)
Goodwill impairment	305		$ 0	$ 118
Corporate and Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill impairment	305			118
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Credit Card
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Additional pretax loss	8
Provision for credit losses	306
Impairment of other assets	2
Valuation allowance on other assets	7
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Credit Card | Corporate and Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill impairment	$ 305	$ 118		$ 118