Other Assets (Intangible Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (112)	$ (109)
Net carrying value	73
Total intangible assets, gross	185	207
Net intangible assets	73	98
Disposal Group, Held-for-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	122
Accumulated amortization	(64)	(53)
Net carrying value	53	69
Customer lists
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	41	58
Accumulated amortization	(39)	(51)
Net carrying value	2	7
Purchased credit card relationships
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	25	25
Accumulated amortization	(7)	(4)
Net carrying value	18	21
Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	2	2
Accumulated amortization	(2)	(1)
Net carrying value	$ 0	$ 1