Derivatives - Marketing Derivatives (Details)	9 Months Ended				12 Months Ended
	Sep. 30, 2021 $ / Barrel	Sep. 30, 2021 $ / Mcfe	Sep. 30, 2021 MMBbls	Sep. 30, 2021 Bcf	Dec. 31, 2020 $ / Barrel	Dec. 31, 2020 $ / Mcfe	Dec. 31, 2020 MMBbls	Dec. 31, 2020 Bcf
Marketing Derivatives | Not Designated as Hedging Instrument
Derivative [Line Items]
Weighted average sales price (dollars per barrel and dollars per million cubic feet)	69.26	5.63			46.05	2.58
Crude oil | Short position
Derivative [Line Items]
Outstanding net volumes on derivatives not designated as hedges (mmbls/bcf) | MMBbls			(29)				(31)
Natural gas | Short position
Derivative [Line Items]
Outstanding net volumes on derivatives not designated as hedges (mmbls/bcf) | Bcf				(120)				(117)