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Restructuring Charges (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring liability	$ 2	$ 5
Operating lease term			10 years
Fayetteville Shale
Restructuring Cost and Reserve [Line Items]
Office consolidation	6	$ 4
Restructuring liability	2
Operating lease term			10 years
Fayetteville Shale \| Lease Termination
Restructuring Cost and Reserve [Line Items]
Office consolidation	$ 3