Other Assets (Schedule of Goodwill) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Goodwill beginning balance	$ 822	$ 343
Goodwill acquired	0	479
Goodwill ending balance	822	822
Operating Segments | Automotive Finance operations
Goodwill [Roll Forward]
Goodwill beginning balance	20	20
Goodwill acquired	0	0
Goodwill ending balance	20	20
Operating Segments | Insurance operations
Goodwill [Roll Forward]
Goodwill beginning balance	27	27
Goodwill acquired	0	0
Goodwill ending balance	27	27
Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	775	296
Goodwill acquired	0	479
Goodwill ending balance	775	775
Ally Credit Card
Goodwill [Roll Forward]
Goodwill beginning balance	479
Goodwill ending balance	479	479
Ally Lending | Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	153
Goodwill ending balance	153	153
Ally Invest | Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance	143
Goodwill ending balance	$ 143	$ 143