Disclosures About Fair Value Measurements (Narrative) (Details) $ in Millions	1 Months Ended		12 Months Ended
	Jul. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2019 USD ($)
Impairment of oil and gas properties			$ 0	$ 77	$ 285
Raton Basin
Impairment of oil and gas properties		$ 77
Contract deficiency	$ 111
Pressure pumping assets
Impairment of Long-Lived Assets to be Disposed of			16
Sand mine
Impairment of Long-Lived Assets to be Disposed of			$ 13
South Texas Divestiture [Member]
Disposal Group, Including Discontinued Operation, Contingent Consideration						$ 450
Proved properties | Raton Basin
Impairment of oil and gas properties		65
Other property and equipment | Raton Basin
Impairment of oil and gas properties		$ 12
Discount rate
Oil and gas contracts			0.044
Contingent Consideration, Cash Receipt, Measurement Input						0.032
Contingent Consideration, Cash Payment, Measurement Input						0.029
Discount rate | Valuation Technique, Discounted Cash Flow [Member] | Significant Unobservable Inputs (Level 3)
Discounted using an annual rate			0.10