Guarantees and Commitments (Financing Commitments) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Guarantor Obligations [Line Items]
Unused revolving credit line commitments and other	$ 10,658	$ 9,156
Commitments to provide capital to investees	1,191	1,112
Construction-lending commitments	168	178
Home equity lines of credit	134	145
Mortgage loan origination commitments	29	14
Unconditionally cancelable unfunded commitments	18,700	$ 23,600
Disposal Group, Held-for-Sale, Not Discontinued Operations | Ally Lending
Guarantor Obligations [Line Items]
Unused revolving credit line commitments and other	$ 68