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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
Sep. 30, 2020
Dec. 31, 2019
Derivatives, Fair Value [Line Items]    
Carrying Amount of Hedged Items $ 24,275 $ 20,397
Cumulative Amount of Fair Value Hedging Adjustments on Hedging Relationships (713) $ (77)
Cumulative fair value adjustment on discontinued hedging relationships $ 197