The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Disclosures About Fair Value Measurements (Measured On A Nonrecurring Basis) (Details) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) $ / MMBTU $ / bbl	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Adjustment		$ 0	$ (77)	$ (285)
Raton Basin
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 186
Fair Value Adjustment	$ (285)
Management oil price outlook \| $ / bbl	53.65
Management gas price outlook \| $ / MMBTU	3.00