Impairment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments	$ 24	$ 75	$ 229
Fair Value, Measurements, Nonrecurring
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment	24	75	229
Fair Value	$ 56	$ 113	179
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