Long-Term Debt - Debt Issuance, Repurchases, Repayments and Exchanges (Details)	9 Months Ended
	Sep. 30, 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 September 30, 2020	37,511,000,000
Variable rate bonds due February 2021 | July Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Tender and purchase	(473,000,000)
Variable rate bonds due February 2021 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Tender and purchase	(122,000,000)
Variable rate bonds due August 2022 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Tender and purchase	$ (448,000,000)
6.500% note payable to WES due 2038 | August Exchange | WES
Long-term Debt Rollforward [Roll Forward]
Interest rate	6.50%
Tender and purchase	$ (260,000,000)
2-year variable rate Term Loan due 2021 | September Repayment
Long-term Debt Rollforward [Roll Forward]
Tender and purchase	$ (500,000,000)
Senior Notes | 8.000% senior notes due 2025 | Issuance of July 2020 Notes
Long-term Debt Rollforward [Roll Forward]
Interest rate	8.00%
Issuances	$ 500,000,000
Senior Notes | 8.500% senior notes due 2027 | Issuance of July 2020 Notes
Long-term Debt Rollforward [Roll Forward]
Interest rate	8.50%
Issuances	$ 500,000,000
Senior Notes | 8.875% senior notes due 2030 | Issuance of July 2020 Notes
Long-term Debt Rollforward [Roll Forward]
Interest rate	8.875%
Issuances	$ 1,000,000,000
Senior Notes | 4.100% senior notes due February 2021 | July Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	4.10%
Tender and purchase	$ (943,000,000)
Senior Notes | 4.100% senior notes due February 2021 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	4.10%
Tender and purchase	$ (139,000,000)
Senior Notes | 4.850% senior notes due March 2021 | July Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	4.85%
Tender and purchase	$ (530,000,000)
Senior Notes | 2.600% senior notes due August 2021 | July Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	2.60%
Tender and purchase	$ (51,000,000)
Senior Notes | 2.600% senior notes due August 2021 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	2.60%
Tender and purchase	$ (1,099,000,000)
Senior Notes | 5.875% senior notes due 2025 | Issuance of August 2020 Notes
Long-term Debt Rollforward [Roll Forward]
Interest rate	5.875%
Issuances	$ 900,000,000
Senior Notes | 6.375% senior notes due 2028 | Issuance of August 2020 Notes
Long-term Debt Rollforward [Roll Forward]
Interest rate	6.375%
Issuances	$ 600,000,000
Senior Notes | 6.625% senior notes due 2030 | Issuance of August 2020 Notes
Long-term Debt Rollforward [Roll Forward]
Interest rate	6.625%
Issuances	$ 1,500,000,000
Senior Notes | 2.600% senior Notes due April 2022 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	2.60%
Tender and purchase	$ (171,000,000)
Senior Notes | 2.700% senior Notes due August 2022 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	2.70%
Tender and purchase	$ (102,000,000)
Senior Notes | 2.700% senior Notes due February 2023 | August and September Tender and Purchase
Long-term Debt Rollforward [Roll Forward]
Interest rate	2.70%
Tender and purchase	$ (52,000,000)