Impairment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments	$ 75	$ 229	$ 67
Dry well costs	35	64	23
Fair Value, Measurements, Nonrecurring
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment	75	229	67
Fair Value		179
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Nonrecurring
Impaired Long-Lived Assets Held and Used [Line Items]
Fair Value	113
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring | International
Impaired Long-Lived Assets Held and Used [Line Items]
Fair Value		103
Impairments		136
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring | Gulf of Mexico Assets
Impaired Long-Lived Assets Held and Used [Line Items]
Fair Value		76
Impairments		89
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring | Oklahoma and Gulf of Mexico
Impaired Long-Lived Assets Held and Used [Line Items]
Fair Value			15
Impairments			$ 67
Rodo
Impaired Long-Lived Assets Held and Used [Line Items]
Dry well costs	$ 32
Diaba
Impaired Long-Lived Assets Held and Used [Line Items]
Dry well costs		$ 64