Other Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Line Items]
Proportional amortization investments	$ 2,131	$ 1,866
Unfunded commitments for proportional amortization investments	$ 1,019	973
Unfunded commitments, period to be paid	5 years
Loss on nonmarketable equity investments, net	$ 6	10	$ 132
Goodwill impairment	118	149	$ 0
Goodwill, transfers		4
Corporate and Other
Goodwill [Line Items]
Goodwill impairment	118	149
Goodwill, transfers		4
Corporate and Other | Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Credit Card
Goodwill [Line Items]
Goodwill impairment	$ 118
Corporate and Other | Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Lending
Goodwill [Line Items]
Goodwill impairment		$ 149