LONG-TERM DEBT - DEBT ISSUANCE, REPURCHASES, REPAYMENTS AND EXCHANGES (Details)	6 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Long-term Debt Rollforward [Roll Forward]
Total borrowings at face value as of December 31, 2019		$ 37,401,000,000
Total borrowings at face value as of December 31, 2020	$ 35,235,000,000	35,235,000,000
Variable rate bonds due February 2021 | July Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		(473,000,000)
Variable rate bonds due February 2021 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		(123,000,000)
Variable rate bonds due August 2022 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (448,000,000)
6.500% note payable to WES due 2038 | August Exchange | WES
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	6.50%	6.50%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (260,000,000)
2-year variable rate term loan due 2021
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments	$ (2,500,000,000)
2-year variable rate term loan due 2021 | September Repayment
Debt Instrument [Line Items]
Debt instrument, term		2 years
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (500,000,000)
2-year variable rate bonds due August 2021 | October Repayment
Debt Instrument [Line Items]
Debt instrument, term		2 years
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (377,000,000)
2-year variable rate term loan due September 2021 | October Repayment
Debt Instrument [Line Items]
Debt instrument, term		2 years
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (1,010,000,000)
2-year variable rate term loan due September 2021 | November Repayment
Debt Instrument [Line Items]
Debt instrument, term		2 years
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (232,000,000)
2-year variable rate term loan due September 2021 | December Repayment
Debt Instrument [Line Items]
Debt instrument, term		2 years
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (214,000,000)
Senior notes
Long-term Debt Rollforward [Roll Forward]
Total borrowings at face value as of December 31, 2020	$ 7,000,000,000.0	$ 7,000,000,000.0
Senior notes | 8.000% senior notes due 2025 | Issuance of July 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	8.00%	8.00%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 500,000,000
Senior notes | 8.500% senior notes due 2027 | Issuance of July 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	8.50%	8.50%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 500,000,000
Senior notes | 8.875% senior notes due 2030 | Issuance of July 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	8.875%	8.875%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 1,000,000,000
Senior notes | 4.100% senior notes due February 2021 | July Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	4.10%	4.10%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (943,000,000)
Senior notes | 4.100% senior notes due February 2021 | August and September Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	4.10%	4.10%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (139,000,000)
Senior notes | 4.100% senior notes due February 2021 | December Repayment
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	4.10%	4.10%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (167,000,000)
Senior notes | 4.850% senior notes due March 2021 | July Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	4.85%	4.85%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (530,000,000)
Senior notes | 2.600% senior notes due August 2021 | July Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.60%	2.60%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (51,000,000)
Senior notes | 2.600% senior notes due August 2021 | August and September Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.60%	2.60%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (1,099,000,000)
Senior notes | 2.600% senior notes due August 2021 | December Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.60%	2.60%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (126,000,000)
Senior notes | 5.875% senior notes due 2025 | Issuance of August 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	5.875%	5.875%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 900,000,000
Senior notes | 6.375% senior notes due 2028 | Issuance of August 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	6.375%	6.375%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 600,000,000
Senior notes | 6.625% senior notes due 2030 | Issuance of August 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	6.625%	6.625%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 1,500,000,000
Senior notes | 2.600% senior notes due April 2022 | August and September Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.60%	2.60%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (171,000,000)
Senior notes | 2.600% senior notes due April 2022 | December Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.60%	2.60%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (128,000,000)
Senior notes | 2.700% senior notes due August 2022 | August and September Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.70%	2.70%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (102,000,000)
Senior notes | 2.700% senior notes due August 2022 | December Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.70%	2.70%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (1,269,000,000)
Senior notes | 2.700% senior notes due February 2023 | August and September Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.70%	2.70%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (52,000,000)
Senior notes | 2.700% senior notes due February 2023 | December Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	2.70%	2.70%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (212,000,000)
Senior notes | 0.00% senior notes due October 2036
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments	$ (2,000,000)
Senior notes | 0.00% senior notes due October 2036 | October Repayment
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	0.00%	0.00%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (2,000,000)
Senior notes | 5.500% senior notes due 2025 | Issuance of December 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	5.50%	5.50%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 750,000,000
Senior notes | 6.125% senior notes due 2031 | Issuance of December 2020 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	6.125%	6.125%
Long-term Debt Rollforward [Roll Forward]
Issuances		$ 1,250,000,000
Senior notes | 3.125% senior notes due February 2022 | December Tender and Purchase
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	3.125%	3.125%
Long-term Debt Rollforward [Roll Forward]
Tender, purchase and repayments		$ (538,000,000)