Leasing (Ally as the Lessor) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Property, Plant, and Equipment, Lessor Asset under Operating Lease [Line Items]
Vehicles	$ 10,565	$ 11,101
Accumulated depreciation	(1,834)	(1,930)
Investment in operating leases, net	$ 8,731	9,171
Minimum
Property, Plant, and Equipment, Lessor Asset under Operating Lease [Line Items]
Lessor, term of contract	24 months
Maximum
Property, Plant, and Equipment, Lessor Asset under Operating Lease [Line Items]
Lessor, term of contract	60 months
Vehicles
Property, Plant, and Equipment, Lessor Asset under Operating Lease [Line Items]
Residual value of leased asset	$ 272	12
Vehicles | 15% Of Manufacturer Suggested Retail Price
Property, Plant, and Equipment, Lessor Asset under Operating Lease [Line Items]
Residual value of leased asset	$ 8	$ 12
Residual value guarantee, percentage	15.00%	15.00%
Vehicles | 50% Of Contract Residual Value
Property, Plant, and Equipment, Lessor Asset under Operating Lease [Line Items]
Residual value of leased asset	$ 264
Residual value guarantee, percentage	50.00%