Disclosures About Fair Value Measurements (Assets And Liabilities That Are Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets	$ 82	$ 95
Investments in Affiliates, Subsidiaries, Associates, and Joint Ventures, Fair Value Disclosure	172
Total assets	306	106
Total liabilities	27	255
Total recurring fair value measurements	279	(149)
Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	52	11
Commodity derivatives	27	255
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets	82	95
Investments in Affiliates, Subsidiaries, Associates, and Joint Ventures, Fair Value Disclosure	0
Total assets	82	95
Total liabilities	0	0
Total recurring fair value measurements	82	95
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	0	0
Commodity derivatives	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets	0	0
Investments in Affiliates, Subsidiaries, Associates, and Joint Ventures, Fair Value Disclosure	172
Total assets	224	11
Total liabilities	27	255
Total recurring fair value measurements	197	(244)
Significant Other Observable Inputs (Level 2) | Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	52	11
Commodity derivatives	27	255
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets	0	0
Total assets	0	0
Total liabilities	0	0
Total recurring fair value measurements	0	0
Significant Unobservable Inputs (Level 3) | Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivatives	0	0
Commodity derivatives	$ 0	$ 0