ACQUISITIONS AND DIVESTITURES - Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Energen
Business Acquisition [Line Items]
Revenues	$ 3,532	$ 2,196
Income (loss) from operations	1,559	900
Net income (loss)	$ 1,320	$ 875
Basic earnings per common share (in dollars per share)	$ 7.54	$ 5.26
Diluted earnings per common share (in dollars per share)	$ 7.53	$ 5.24
Delaware Basin Interests
Business Acquisition [Line Items]
Revenues		$ 1,228	$ 627
Income (loss) from operations		619	(13)
Net income (loss)		$ 473	$ (109)
Basic earnings per common share (in dollars per share)		$ 4.85	$ (1.45)
Diluted earnings per common share (in dollars per share)		$ 4.84	$ (1.45)