ACQUISITIONS AND DIVESTITURES - Estimated Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	Nov. 29, 2018	Dec. 31, 2018	Feb. 28, 2017
Energen
Business Acquisition [Line Items]
Consideration	$ 7,136
Fair value of liabilities assumed:
Current liabilities	388
Asset retirement obligations	(105)
Long-term debt	1,099
Noncurrent derivative instruments	17
Deferred income taxes	1,425	$ 1,400
Other long-term liabilities	7
Amount attributable to liabilities assumed	3,041
Fair value of assets acquired:
Total current assets	298
Oil and natural gas properties	9,361
Midstream assets	253
Investment in real estate	11
Other property, equipment and land	58
Asset retirement obligation	105
Other postretirement assets	3
Noncurrent income tax receivable, net	76
Other long term assets	12
Amount attributable to assets acquired	$ 10,177
Delaware Basin Interests
Fair value of liabilities assumed:
Asset retirement obligations			$ (2)
Revenues and royalties payable			(10)
Fair value of assets acquired:
Proved oil and natural gas properties			386
Unevaluated oil and natural gas properties			2,123
Midstream assets			47
Prepaid capital costs			4
Oil inventory			1
Total fair value of net assets			$ 2,549