INCOME TAXES - Net Deferred Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
U.S. and state net operating losses	$ 2,306	$ 2,108
Capital losses	633	626
Tax credits and other tax incentives	33	32
Foreign tax credits	2,241	2,241
Accrued expenses and liabilities	93	97
Asset retirement obligation	654	618
Property & equipment	261	0
Investment in Altus Midstream LP	76	107
Net interest expense limitation	252	162
Lease liability	79	108
Other	1	88
Total deferred tax assets	6,629	6,187
Valuation allowance	(5,991)	(4,959)	$ (3,947)	$ (3,816)
Net deferred tax assets	638	1,228
Deferred tax liabilities:
Deferred income	0	1
Equity investments	4	0
Property and equipment	750	1,432
Right-of-use asset	74	106
Other	13	6
Total deferred tax liabilities	841	1,545
Net deferred income tax liability	$ 203	$ 317