Held-for-sale Operations - Schedule of Fair Value Measurements - Nonrecurring Basis (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
	Dec. 31, 2024	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2024
Assets
Total assets	$ 0	$ 2,440	$ 0		$ 0
Liabilities
Total liabilities	0	35	0		0
Goodwill impairment		305		$ 0	118
Corporate and Other
Liabilities
Goodwill impairment		305			118
Nonrecurring fair value measurements
Liabilities
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	0	0	0		0
Goodwill impairment	$ 118
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Credit Card
Assets
Loans held-for-sale, net		2,248
Other assets		192
Total assets		2,440
Liabilities
Accrued expenses and other liabilities		35
Total liabilities		35
Impairment of other assets		2
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Credit Card | Corporate and Other
Liabilities
Goodwill impairment		305	$ 118		$ 118
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Nonrecurring fair value measurements | Ally Credit Card
Assets
Loans held-for-sale, net		2,248
Other assets		199
Total assets		2,447
Liabilities
Accrued expenses and other liabilities		35
Total liabilities		35
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments		(307)
Total gain (loss) included in earnings		(7)
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Level 1 | Nonrecurring fair value measurements | Ally Credit Card
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 Credit Card
Assets
Loans held-for-sale, net		2,248
Other assets		199
Total assets		2,447
Liabilities
Accrued expenses and other liabilities		35
Total liabilities		35
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Level 3 | Nonrecurring fair value measurements | Ally Credit Card
Assets
Loans held-for-sale, net		0
Other assets		0
Total assets		0
Liabilities
Accrued expenses and other liabilities		0
Total liabilities		$ 0