Other Assets (Schedule of Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Goodwill beginning balance	$ 822	$ 822
Goodwill acquired		0
Goodwill impairment	(149)	0	$ 0
Transfer to assets of operations held-for-sale	(4)
Goodwill ending balance	669	822	822
Operating Segments | Automotive Finance operations
Goodwill [Roll Forward]
Goodwill beginning balance	20	20
Goodwill acquired		0
Goodwill impairment	0
Transfer to assets of operations held-for-sale	0
Goodwill ending balance	20	20	20
Operating Segments | Insurance operations
Goodwill [Roll Forward]
Goodwill beginning balance	27	27
Goodwill acquired		0
Goodwill impairment	0
Transfer to assets of operations held-for-sale	0
Goodwill ending balance	27	27	27
Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	775	775
Goodwill acquired		0
Goodwill impairment	(149)
Transfer to assets of operations held-for-sale	(4)
Goodwill ending balance	622	775	$ 775
Ally Credit Card | Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	479
Goodwill ending balance	479	479
Ally Invest | Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	143
Goodwill ending balance	143	143
Ally Lending | Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	$ 153
Goodwill ending balance		$ 153