Derivative Financial Instruments - Balance Sheet Location of GM Financial Unsecured Debt (Details) - Fair Value Hedges [Member] - Long-term Debt [Member] - GM Financial [Member] - USD ($) $ in Millions |
Jun. 30, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Derivatives, Fair Value [Line Items] | ||
| Carrying Amount of Hedged Items | $ 24,203 | $ 20,397 |
| Cumulative Amount of Fair Value Hedging Adjustments on Hedging Relationships | $ (648) | $ (77) |