DERIVATIVES - FAIR VALUE (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Oil Collars and Calls | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	$ 0	$ 0
Total fair value, asset	25	92
Oil Collars and Calls | Other current assets | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Oil Collars and Calls | Other current assets | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	25	92
Oil Collars and Calls | Other current assets | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Oil Collars and Calls | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting, liability	0
Total fair value, liability	(42)
Oil Collars and Calls | Accrued liabilities | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Oil Collars and Calls | Accrued liabilities | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(42)
Oil Collars and Calls | Accrued liabilities | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Oil Collars and Calls | Deferred credits and other liabilities - other
Gross and net fair values of outstanding derivatives (in millions)
Netting, liability		0
Total fair value, liability		(160)
Oil Collars and Calls | Deferred credits and other liabilities - other | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		0
Oil Collars and Calls | Deferred credits and other liabilities - other | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		(160)
Oil Collars and Calls | Deferred credits and other liabilities - other | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		0
Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Initial margin	85	65
Marketing Derivatives | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(1,204)	(973)
Total fair value, asset	31	51
Marketing Derivatives | Other current assets | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	1,155	945
Marketing Derivatives | Other current assets | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	80	79
Marketing Derivatives | Other current assets | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Marketing Derivatives | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(7)	(4)
Total fair value, asset	2	12
Marketing Derivatives | Long-term receivables and other assets, net | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	7	4
Marketing Derivatives | Long-term receivables and other assets, net | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	2	12
Marketing Derivatives | Long-term receivables and other assets, net | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Marketing Derivatives | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting, liability	1,204	973
Total fair value, liability	(129)	(79)
Marketing Derivatives | Accrued liabilities | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(1,252)	(1,008)
Marketing Derivatives | Accrued liabilities | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(81)	(44)
Marketing Derivatives | Accrued liabilities | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Marketing Derivatives | Deferred credits and other liabilities - other
Gross and net fair values of outstanding derivatives (in millions)
Netting, liability	7	4
Total fair value, liability	0	(1)
Marketing Derivatives | Deferred credits and other liabilities - other | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(7)	(4)
Marketing Derivatives | Deferred credits and other liabilities - other | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	(1)
Marketing Derivatives | Deferred credits and other liabilities - other | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Collateral paid netted against derivative liabilities	374
Interest Rate Swaps | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset		0
Total fair value, asset		5
Interest Rate Swaps | Other current assets | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Interest Rate Swaps | Other current assets | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		5
Interest Rate Swaps | Other current assets | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Interest Rate Swaps | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset		0
Total fair value, asset		5
Interest Rate Swaps | Long-term receivables and other assets, net | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Interest Rate Swaps | Long-term receivables and other assets, net | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		5
Interest Rate Swaps | Long-term receivables and other assets, net | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Interest Rate Swaps | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting, liability	0	0
Total fair value, liability	(936)	(657)
Interest Rate Swaps | Accrued liabilities | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Interest Rate Swaps | Accrued liabilities | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(936)	(657)
Interest Rate Swaps | Accrued liabilities | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Interest Rate Swaps | Deferred credits and other liabilities - other
Gross and net fair values of outstanding derivatives (in millions)
Netting, liability	0	0
Total fair value, liability	(822)	(776)
Interest Rate Swaps | Deferred credits and other liabilities - other | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Interest Rate Swaps | Deferred credits and other liabilities - other | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(822)	(776)
Interest Rate Swaps | Deferred credits and other liabilities - other | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	$ 0	0
Berkshire Warrants | Deferred credits and other liabilities - other
Gross and net fair values of outstanding derivatives (in millions)
Netting, liability		0
Total fair value, liability		(107)
Berkshire Warrants | Deferred credits and other liabilities - other | Level 1
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		0
Berkshire Warrants | Deferred credits and other liabilities - other | Level 2
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		(107)
Berkshire Warrants | Deferred credits and other liabilities - other | Level 3
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		$ 0