Leasing - Ally as the Lessee (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Dec. 31, 2025 |
|
| 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 | $ 10 | $ 9 | $ 19 | $ 18 | |
| Right-of-use asset obtained in exchange for operating lease liability | $ 7 | $ 6 | |||
| Operating lease, weighted-average remaining lease term | 5 years | 5 years | 5 years | ||
| Operating lease, weighted average discount rate | 3.70% | 3.70% | 3.66% | ||
| Minimum | |||||
| Lessee, Lease, Description [Line Items] | |||||
| Operating lease remaining lease term | 2 months | 2 months | |||
| Maximum | |||||
| Lessee, Lease, Description [Line Items] | |||||
| Operating lease remaining lease term | 10 years | 10 years | |||