Other Assets - Schedule of Schedule of Goodwill (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Goodwill beginning balance	$ 669	$ 822
Goodwill impairment		(149)
Transfer to assets of operations held-for-sale		(4)
Goodwill acquired	0
Goodwill ending balance	669	669
Operating Segments | Automotive Finance operations
Goodwill [Roll Forward]
Goodwill beginning balance	20	20
Goodwill impairment		0
Transfer to assets of operations held-for-sale		0
Goodwill acquired	0
Goodwill ending balance	20	20
Operating Segments | Insurance operations
Goodwill [Roll Forward]
Goodwill beginning balance	27	27
Goodwill impairment		0
Transfer to assets of operations held-for-sale		0
Goodwill acquired	0
Goodwill ending balance	27	27
Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	622	775
Goodwill impairment		(149)
Transfer to assets of operations held-for-sale		(4)
Goodwill acquired	0
Goodwill ending balance	622	622
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