Held-for-sale Operations - Schedule of Fair Value Measurements - Nonrecurring Basis (Details) - USD ($) $ in Millions		12 Months Ended
	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Assets
Total assets	$ 0	$ 0	$ 1,975
Liabilities
Total liabilities	0	0	17
Goodwill impairment		118	149	$ 0
Corporate and Other
Liabilities
Goodwill impairment		118	149
Nonrecurring fair value measurements
Liabilities
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	0	$ 0	0
Goodwill impairment	$ 118
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Lending
Assets
Loans held-for-sale, net			1,940
Other assets			35
Total assets			1,975
Liabilities
Accrued expenses and other liabilities			17
Total liabilities			17
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Lending | Corporate and Other
Liabilities
Goodwill impairment			149
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Nonrecurring fair value measurements | Ally Lending
Assets
Loans held-for-sale, net			1,940
Other assets			35
Total assets			1,975
Liabilities
Accrued expenses and other liabilities			17
Total liabilities			17
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments			(149)
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Level 1 | Nonrecurring fair value measurements | Ally Lending
Assets
Loans held-for-sale, net			0
Other assets			0
Total assets			0
Liabilities
Accrued expenses and other liabilities			0
Total liabilities			0
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Level 2 | Nonrecurring fair value measurements | Ally Lending
Assets
Loans held-for-sale, net			1,940
Other assets			35
Total assets			1,975
Liabilities
Accrued expenses and other liabilities			17
Total liabilities			17
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Level 3 | Nonrecurring fair value measurements | Ally Lending
Assets
Loans held-for-sale, net			0
Other assets			0
Total assets			0
Liabilities
Accrued expenses and other liabilities			0
Total liabilities			$ 0