Acquisitions and Divestitures (Divestitures and Decommissioning Activities) (Details) $ in Millions	1 Months Ended							12 Months Ended
	Dec. 31, 2018 USD ($)	Nov. 30, 2018 USD ($)	Aug. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Apr. 30, 2018 USD ($) a	Apr. 30, 2017 USD ($) a	Dec. 31, 2019 USD ($) a	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration								$ 56
Gain (loss) on disposition of assets, net								(477)	$ 290	$ 208
Proceeds from disposition of assets, net of cash sold								149	469	352
Accelerated depreciation								23	443	0
Impairment of Oil and Gas Properties								$ 0	(77)	(285)
Sinor Nest
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of assets, net	$ 54
Area of Land | a								2,900
Proceeds from disposition of assets, net of cash sold	$ 105
Sand mine
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Employee-related charges		$ 7
Accelerated depreciation								$ 23
West Panhandle
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of assets, net			$ 127
Employee-related charges			7
Proceeds from disposition of assets, net of cash sold			$ 170
Raton Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of assets, net				$ 2
Employee-related charges				6
Other divestiture-related charges				117
Proceeds from disposition of assets, net of cash sold				54
Impairment of Oil and Gas Properties					$ (77)
Contract deficiency				$ 111
West Eagle Ford Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of assets, net						$ 75
Area of Land | a						10,200
Proceeds from disposition of assets, net of cash sold						$ 100
Martin County
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of assets, net							$ 194
Proceeds from disposition of assets, net of cash sold							$ 264
Acres sold | a							20,500
Other proved and unproved properties, inventory and other property and equipment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of assets, net								$ (9)	1	$ 14
Permian Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from disposition of assets, net of cash sold									$ 77