Derivative and Hedging Activities - Derivative Instruments in Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Total derivatives	$ (118)	$ 130
Not designated as hedging instrument \| Commodity contracts
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset		130
Derivative liability, fair value, gross liability	(118)
Derivative liability, fair value, gross asset	0	0
Total derivatives	(118)	130
Not designated as hedging instrument \| Commodity contracts \| Short-term derivative asset
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	84	174
Derivative asset, fair value, gross liability	(65)	(40)
Total derivatives	19	134
Not designated as hedging instrument \| Commodity contracts \| Long-term derivative asset
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	5
Derivative asset, fair value, gross liability	(5)
Total derivatives	0
Not designated as hedging instrument \| Commodity contracts \| Short-term derivative liability
Derivatives, Fair Value [Line Items]
Derivative liability, fair value, gross liability	(158)	(42)
Derivative liability, fair value, gross asset	65	40
Total derivatives	(93)	(2)
Not designated as hedging instrument \| Commodity contracts \| Long-term derivative liability
Derivatives, Fair Value [Line Items]
Derivative liability, fair value, gross liability	(49)	(2)
Derivative liability, fair value, gross asset	5	0
Total derivatives	$ (44)	$ (2)

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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