Held-for-sale Operations - Schedule of Fair Value Measurements - Nonrecurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Jun. 30, 2024
Assets
Total assets	$ 1,975	$ 0
Liabilities
Total liabilities	17	0
Goodwill impairment	149
Corporate and Other
Liabilities
Goodwill impairment	149
Nonrecurring fair value measurements
Liabilities
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	0	$ 0
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