INVESTMENTS AND RELATED-PARTY TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Method Investments
Equity method investment amounts				$ 3,250	$ 6,389	$ 1,680
Goodwill impairment loss		$ 1,200
Cumulative undistributed earnings (loss)				(166)	(40)
Equity investments dividends paid				678	422	329
Excess of investments in equity investees over the underlying equity in net assets				649
Excess of investments in equity investees over the underlying equity in net assets, which represents goodwill				326
Equity-method investments financial information summarized by Income Statement line item
Revenues and other income				16,261	21,750	18,934
Costs and expenses				31,913	22,002	13,657
Net income				(15,652)	(252)	5,277
Equity-method investments financial information summarized by Balance Sheet line item
Current assets				8,819	14,633
Current liabilities				8,223	12,705
Long-term debt				35,745	38,537
Other non-current liabilities				17,523	21,716
Stockholders’ equity				18,573	34,232
RELATED-PARTY TRANSACTIONS
Sales				301	691	805
Purchases				1,112	463	502
Services (d)				1,032	28	52
Advances and amounts due from related parties				54	133	63
Amounts due to related parties				273	463	46
Equity Method Investment, Nonconsolidated Investee
Equity-method investments financial information summarized by Income Statement line item
Revenues and other income				5,455	26,520	28,091
Costs and expenses				5,455	24,084	25,029
Net income				0	2,436	3,062
Equity-method investments financial information summarized by Balance Sheet line item
Current assets				1,419	1,130	5,587
Non-current assets				18,693	21,158	25,871
Current liabilities				1,549	785	4,879
Long-term debt				7,860	8,673	12,505
Other non-current liabilities				866	859	95
Stockholders’ equity				9,837	11,971	$ 13,979
Anadarko Petroleum Corporation
Equity Method Investments
Equity method investment amounts				2,900
WES
Equity Method Investments
Equity method investment amounts				$ 1,930	$ 5,100
Equity method investment ownership percentage				53.50%
Goodwill impairment loss		$ 1,200
Other-than-temporary impairment loss	$ 2,700		$ 2,700
RELATED-PARTY TRANSACTIONS
Sales to related party (as a percent)				70.00%
Purchases from related party (as a percent)				59.00%
OxyChem Ingleside Facility
Equity Method Investments
Equity method investment amounts				$ 635
Equity method investment ownership percentage				50.00%
Dolphin Energy Limited
Equity Method Investments
Equity method investment amounts				$ 290
Equity method investment ownership percentage				24.50%
Other
Equity Method Investments
Equity method investment amounts				$ 395
General Partner of Plains All American Pipeline, L.P
RELATED-PARTY TRANSACTIONS
Sales to related party (as a percent)					87.00%	89.00%
Plains All American Pipeline, LP
Equity-method investments financial information summarized by Balance Sheet line item
Investment gross revenue					$ 24,700
Ingleside Ethylene LLC
RELATED-PARTY TRANSACTIONS
Purchases from related party (as a percent)				41.00%	98.00%	98.00%