Regulatory Capital and Other Regulatory Matters - Depository Institutions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total assets	$ 191,836	$ 196,329	$ 191,826
Statutory accounting practices, statutory amount available for dividend payments	116
Ally Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total assets	181,400	186,100
Payments of dividends	$ 1,200	$ 1,400