Acquisition and Divestitures (Narrative) (Details) $ in Millions, $ in Billions				3 Months Ended								12 Months Ended			48 Months Ended
		Feb. 28, 2021 USD ($)	Oct. 01, 2020 USD ($) $ / MMBTU $ / bbl	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) MMBoe	Jun. 30, 2020 USD ($)	Jun. 30, 2020 CAD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 CAD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2020 USD ($) MMBoe	Dec. 31, 2019 USD ($) MMBoe	Dec. 31, 2018 USD ($) MMBoe	Dec. 31, 2024	Jan. 07, 2021 USD ($) shares	Apr. 30, 2020 USD ($)
Business Acquisition [Line Items]
Common Stock Shares Issued					$ 38			$ 38				$ 38	$ 38
Asset impairment charges												182	785
Gain recognized on sale of business, pre tax												$ (1)	$ 222	$ 2,593
Total estimated proved reserves | MMBoe	[1]											2	54	24
Gain on asset dispositions												$ 1	$ 48	$ 278
Non Core Assets [Member]
Business Acquisition [Line Items]
Divestitures of property and equipment					$ 12								$ 390	$ 500
Total estimated proved reserves | MMBoe					3								54	24
Gain on asset dispositions													$ 48	$ 278
Non Core Assets [Member] | Johnson County and Wise County Texas [Member]
Business Acquisition [Line Items]
Divestitures of property and equipment														500
Gain recognized on sale of business, pre tax														26
Settlement expenses relating to gas processing contracts														40
EnLink and General Partner [Member]
Business Acquisition [Line Items]
Proceeds from sale of business											$ 3,125			3,125
Gain recognized on sale of business, pre tax											2,600			2,600
Gain recognized on sale of business, net of tax											$ 2,200			$ 2,200
Barnett Shale [Member]
Business Acquisition [Line Items]
Cash deposit received																	$ 170
Divestitures of property and equipment			$ 490
Contingent earnout payments			$ 260
Henry Hub gas price for contingent earnout payment upside | $ / MMBTU			2.75
WTI oil price for contingent earnout payment upside | $ / bbl			50
Asset impairment charges								$ 748				$ 182	748
Canadian Business Segment [Member]
Business Acquisition [Line Items]
Proceeds from sale of business									$ 2,600	$ 3.4
Gain recognized on sale of business, pre tax									223
Gain recognized on sale of business, net of tax									$ 425
Canadian Business Segment [Member] | Canadian Natural Resources Limited [Member]
Business Acquisition [Line Items]
Proceeds from sale of business						$ 2,600	$ 3.4
Gain recognized on sale of business, pre tax													223
Gain recognized on sale of business, net of tax													$ 425
Scenario Forecast [Member] | Non Core Assets [Member]
Business Acquisition [Line Items]
Contingent earnout payments				$ 8
Scenario Forecast [Member] | Barnett Shale [Member]
Business Acquisition [Line Items]
Contingent earnout payment period															The contingent payment period commences on January 1, 2021 and has a term of four years.
Subsequent Event [Member]
Business Acquisition [Line Items]
Common Stock Shares Issued																$ 5,400
Devon and WPX Agreement [Member]
Business Acquisition [Line Items]
Date of Agreement												Jan. 07, 2021
Common Stock Shares Issued					$ 5,400							$ 5,400
Devon and WPX Agreement [Member] | Scenario Forecast [Member]
Business Acquisition [Line Items]
Redemption of bond		$ 43
Premium paid on redemption of bonds		$ 2
Devon and WPX Agreement [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Per share conversion | shares																0.5165

[1] Gas reserves are converted to Boe at the rate of six Mcf per Bbl of oil, based upon the approximate relative energy content of gas and oil. NGL reserves are converted to Boe on a one-to-one basis with oil. The conversion rates are not necessarily indicative of the relationship of oil, natural gas and NGL prices.