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Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jul. 31, 2018	Jul. 31, 2016	Jan. 31, 2015
Debt Instrument [Line Items]
Impairments	$ 2	$ 161	$ 8	$ 171
Long-term debt \| 4.05% Senior Notes due January 2020
Debt Instrument [Line Items]
Stated interest rate	6.05%		6.05%		5.30%	5.80%	4.05%
Long-term debt \| 4.05% Senior Notes due January 2020 \| Significant Other Observable Inputs (Level 2)
Debt Instrument [Line Items]
Stated interest rate							3.42%
Fayetteville Shale
Debt Instrument [Line Items]
Impairments		161		161
Midstream
Debt Instrument [Line Items]
Impairments	$ 2	145	$ 2	155
Midstream \| Fayetteville Shale
Debt Instrument [Line Items]
Impairments		145		145
E&P
Debt Instrument [Line Items]
Impairments	$ 0	15	$ 6	15
E&P \| Fayetteville Shale
Debt Instrument [Line Items]
Impairments		15		15
Non-Core Assets
Debt Instrument [Line Items]
Impairments		$ 1		$ 1