Leasing (Ally as the Lessee) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Apr. 30, 2021
Lessee, Lease, Description [Line Items]
Noncancelable lease term		367 days
Lease extension, maximum		48 months
Cash paid for amounts included in the measurement of lease liabilities		$ 38	$ 51
Right-of-use asset obtained in exchange for operating lease liability		$ 41	$ 361
Operating lease, weighted-average remaining lease term		5 years	6 years
Operating lease, weighted average discount rate		2.57%	1.96%
Undiscounted future lease payments		$ 3,051		$ 13
Term of contract				10 years
Lease income		$ 1
Minimum
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term		8 months
Term of contract		24 months
Maximum
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term		8 years
Option to terminate		6 years
Term of contract		60 months
Land and Building | Minimum
Lessee, Lease, Description [Line Items]
Option to extend		1 year
Land and Building | Maximum
Lessee, Lease, Description [Line Items]
Option to extend		15 years
Operations Center
Lessee, Lease, Description [Line Items]
Net property and equipment	$ 44