Derivative and Hedging Activities - Derivative Instruments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Bcf MMBbls	Dec. 31, 2019 USD ($) Bcf MMBbls
Derivative [Line Items]
Total derivatives	$ (118)	$ 130
Energy related derivative
Derivative [Line Items]
Total derivatives	$ (118)	$ 130
Energy related derivative | Oil
Derivative [Line Items]
Notional, volume | MMBbls	34,000,000	34
Total derivatives	$ (137)	$ 5
Energy related derivative | Oil | Fixed-price swaps
Derivative [Line Items]
Notional, volume | MMBbls	27,000,000	24
Total derivatives	$ (136)	$ (7)
Energy related derivative | Oil | Collars
Derivative [Line Items]
Notional, volume | MMBbls	0	2
Total derivatives	$ 0	$ 14
Energy related derivative | Oil | Basis protection swaps
Derivative [Line Items]
Notional, volume | MMBbls	7,000,000	8
Total derivatives	$ (1)	$ (2)
Energy related derivative | Natural gas
Derivative [Line Items]
Notional, volume | Bcf	847,000,000	346
Total derivatives	$ 19	$ 125
Energy related derivative | Natural gas | Fixed-price swaps
Derivative [Line Items]
Notional, volume | Bcf	728,000,000	265
Total derivatives	$ 10	$ 125
Energy related derivative | Natural gas | Collars
Derivative [Line Items]
Notional, volume | Bcf	53,000,000	0
Total derivatives	$ 8	$ 0
Energy related derivative | Natural gas | Call options (sold)
Derivative [Line Items]
Notional, volume | Bcf	0	22
Total derivatives	$ 0	$ 0
Energy related derivative | Natural gas | Call swaptions
Derivative [Line Items]
Notional, volume | Bcf	0	29
Total derivatives	$ 0	$ (2)
Energy related derivative | Natural gas | Basis protection swaps
Derivative [Line Items]
Notional, volume | Bcf	66,000,000	30
Total derivatives	$ 1	$ 2