Other Assets (Schedule of Goodwill) (Details) - USD ($) $ in Millions		12 Months Ended
	Apr. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill beginning balance		$ 343	$ 393
Impairment losses		0	(50)	$ 0
Goodwill acquired		479
Goodwill ending balance		822	343	393
Operating Segments | Automotive Finance operations
Goodwill [Roll Forward]
Goodwill beginning balance		20	20
Impairment losses			0
Goodwill acquired		0
Goodwill ending balance		20	20	20
Operating Segments | Insurance operations
Goodwill [Roll Forward]
Goodwill beginning balance		27	27
Impairment losses			0
Goodwill acquired		0
Goodwill ending balance		27	27	27
Corporate and Other
Goodwill [Roll Forward]
Goodwill beginning balance		296	346
Impairment losses	$ (50)		(50)
Goodwill acquired		479
Goodwill ending balance		775	296	$ 346
Fair Square Financial Holdings LLC
Goodwill [Roll Forward]
Goodwill ending balance		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
Impairment losses			(50)
Goodwill ending balance		$ 143	$ 143