Other Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (127)	$ (112)
Net carrying value	58
Total intangible assets, gross	185	185
Net intangible assets	58	73
Disposal Group, Held-for-Sale or Disposed of by Sale, Not Discontinued Operations | Ally Lending
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets		22
Accumulated amortization		22
Technology
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	117	117
Accumulated amortization	(74)	(64)
Net carrying value	43	53
Customer lists
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	41	41
Accumulated amortization	(41)	(39)
Net carrying value	0	2
Purchased credit card relationships
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	25	25
Accumulated amortization	(10)	(7)
Net carrying value	15	18
Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	2	2
Accumulated amortization	(2)	(2)
Net carrying value	$ 0	$ 0