GUARANTOR FINANCIAL STATEMENTS - Cash Flow Statement (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	$ 2,734	$ 1,565	$ 889
Cash flows from investing activities:
Additions to oil and natural gas properties	(2,677)	(1,461)	(793)
Additions to midstream assets	(244)	(204)	(68)
Purchase of other property, equipment and land	(5)	(7)	(23)
Acquisition of leasehold interests	(443)	(1,371)	(1,961)
Acquisition of mineral interests	(333)	(440)	(407)
Acquisition of midstream assets	0	0	(50)
Proceeds from sale of assets	300	80	66
Investment in real estate	(1)	(111)	0
Funds held in escrow	0	11	104
Equity investments	(485)	0	0
Intercompany transfers	0	0	0
Net cash used in investing activities	(3,888)	(3,503)	(3,132)
Cash flows from financing activities:
Proceeds from borrowings under credit facility	2,350	2,652	754
Repayment under credit facility	(3,718)	(1,242)	(384)
Purchase of subsidiary units by parent			0
Repayment on Energen's credit facility	0	(559)	0
Proceeds from senior notes	3,469	1,062	0
Repayment of senior notes	(1,250)	0	0
Premium on extinguishment of debt	(44)	0	0
Proceeds from joint venture	39	0	0
Debt issuance costs	(18)	(25)	(9)
Public offering costs	(41)	(3)	(1)
Proceeds from public offerings	1,106	305	370
Contributions to subsidiaries		0
Distribution to parent		0
Distributions from subsidiary	0	0	0
Proceeds from exercise of stock options	9	0	0
Repurchased for tax withholdings	(13)	(14)	0
Repurchased as part of share buyback	593	0	0
Dividends to stockholders	(112)	(37)	0
Distributions to non-controlling interest	(122)	(98)	(41)
Intercompany transfers	0	0
Net cash (used in) provided by financing activities	1,062	2,041	689
Net increase (decrease) in cash and cash equivalents	(92)	103	(1,554)
Cash and cash equivalents at beginning of period	215	112	1,666
Cash and cash equivalents at end of period	123	215	112
Eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	0	0	0
Cash flows from investing activities:
Additions to oil and natural gas properties	0	0	0
Additions to midstream assets	0	0	0
Purchase of other property, equipment and land	0	0	0
Acquisition of leasehold interests	0	0	0
Acquisition of mineral interests	190	0	0
Acquisition of midstream assets			0
Proceeds from sale of assets	(190)	0	0
Investment in real estate	0	0
Funds held in escrow		0	0
Equity investments	0
Intercompany transfers	0	0	0
Net cash used in investing activities	0	0	0
Cash flows from financing activities:
Proceeds from borrowings under credit facility	0	0	0
Repayment under credit facility	0	0	0
Purchase of subsidiary units by parent			10
Repayment on Energen's credit facility		0
Proceeds from senior notes	0	0
Repayment of senior notes	0
Premium on extinguishment of debt	0
Proceeds from joint venture	0
Debt issuance costs	0	0	0
Public offering costs	0	0	0
Proceeds from public offerings	0	0	(10)
Contributions to subsidiaries		2
Distribution to parent		(155)
Distributions from subsidiary	(860)	0	(89)
Proceeds from exercise of stock options	0
Repurchased for tax withholdings	0	0
Repurchased as part of share buyback	0
Dividends to stockholders	0	0
Distributions to non-controlling interest	860	155	89
Intercompany transfers	0	(2)
Net cash (used in) provided by financing activities	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Parent | Reportable Legal Entities
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	(956)	(58)	(29)
Cash flows from investing activities:
Additions to oil and natural gas properties	0	0	0
Additions to midstream assets	0	0	0
Purchase of other property, equipment and land	0	0	0
Acquisition of leasehold interests	0	0	0
Acquisition of mineral interests	0	0	0
Acquisition of midstream assets			0
Proceeds from sale of assets	0	0	0
Investment in real estate	0	0
Funds held in escrow		0	0
Equity investments	0
Intercompany transfers	(860)	(367)	(1,631)
Net cash used in investing activities	(860)	(367)	(1,631)
Cash flows from financing activities:
Proceeds from borrowings under credit facility	0	0	0
Repayment under credit facility	0	0	0
Purchase of subsidiary units by parent			(10)
Repayment on Energen's credit facility		0
Proceeds from senior notes	2,968	1,062
Repayment of senior notes	(1,250)
Premium on extinguishment of debt	(44)
Proceeds from joint venture	0
Debt issuance costs	0	(14)	(8)
Public offering costs	0	0	0
Proceeds from public offerings	0	0	0
Contributions to subsidiaries		(1)
Distribution to parent		155
Distributions from subsidiary	860	(696)	90
Proceeds from exercise of stock options	9
Repurchased for tax withholdings	(13)	(14)
Repurchased as part of share buyback	593
Dividends to stockholders	(112)	(37)
Distributions to non-controlling interest	0	0	0
Intercompany transfers	0	0
Net cash (used in) provided by financing activities	1,825	455	72
Net increase (decrease) in cash and cash equivalents	9	30	(1,588)
Cash and cash equivalents at beginning of period	84	54	1,642
Cash and cash equivalents at end of period	93	84	54
Guarantor Subsidiaries | Reportable Legal Entities
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	1,433	1,224	768
Cash flows from investing activities:
Additions to oil and natural gas properties	(2,038)	(1,461)	(790)
Additions to midstream assets	(38)	(21)	0
Purchase of other property, equipment and land	0	(7)	(22)
Acquisition of leasehold interests	(360)	(1,371)	(1,961)
Acquisition of mineral interests	0	0	(63)
Acquisition of midstream assets			0
Proceeds from sale of assets	118	79	66
Investment in real estate	0	0
Funds held in escrow		27	(27)
Equity investments	0
Intercompany transfers	0	989	1,631
Net cash used in investing activities	(2,318)	(1,765)	(1,166)
Cash flows from financing activities:
Proceeds from borrowings under credit facility	1,292	1,960	475
Repayment under credit facility	(2,769)	(867)	(78)
Purchase of subsidiary units by parent			0
Repayment on Energen's credit facility		0
Proceeds from senior notes	0	0
Repayment of senior notes	0
Premium on extinguishment of debt	0
Proceeds from joint venture	0
Debt issuance costs	0	0	1
Public offering costs	0	0	0
Proceeds from public offerings	0	0	0
Contributions to subsidiaries		0
Distribution to parent		0
Distributions from subsidiary	0	0	0
Proceeds from exercise of stock options	0
Repurchased for tax withholdings	0	0
Repurchased as part of share buyback	0
Dividends to stockholders	0	0
Distributions to non-controlling interest	0	0	0
Intercompany transfers	2,360	(550)
Net cash (used in) provided by financing activities	883	543	398
Net increase (decrease) in cash and cash equivalents	(2)	2	0
Cash and cash equivalents at beginning of period	2	0	0
Cash and cash equivalents at end of period	0	2	0
Non-Guarantor Subsidiaries | Reportable Legal Entities
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	2,257	399	150
Cash flows from investing activities:
Additions to oil and natural gas properties	(639)	0	(3)
Additions to midstream assets	(206)	(183)	(68)
Purchase of other property, equipment and land	(5)	0	(1)
Acquisition of leasehold interests	(83)	0	0
Acquisition of mineral interests	(523)	(440)	(344)
Acquisition of midstream assets			(50)
Proceeds from sale of assets	372	1	0
Investment in real estate	(1)	(111)
Funds held in escrow		(16)	131
Equity investments	(485)
Intercompany transfers	860	(622)	0
Net cash used in investing activities	(710)	(1,371)	(335)
Cash flows from financing activities:
Proceeds from borrowings under credit facility	1,058	692	279
Repayment under credit facility	(949)	(375)	(306)
Purchase of subsidiary units by parent			0
Repayment on Energen's credit facility		(559)
Proceeds from senior notes	501	0
Repayment of senior notes	0
Premium on extinguishment of debt	0
Proceeds from joint venture	39
Debt issuance costs	(18)	(11)	(2)
Public offering costs	(41)	(3)	(1)
Proceeds from public offerings	1,106	305	380
Contributions to subsidiaries		(1)
Distribution to parent		0
Distributions from subsidiary	0	696	(1)
Proceeds from exercise of stock options	0
Repurchased for tax withholdings	0	0
Repurchased as part of share buyback	0
Dividends to stockholders	0	0
Distributions to non-controlling interest	(982)	(253)	(130)
Intercompany transfers	(2,360)	552
Net cash (used in) provided by financing activities	(1,646)	1,043	219
Net increase (decrease) in cash and cash equivalents	(99)	71	34
Cash and cash equivalents at beginning of period	129	58	24
Cash and cash equivalents at end of period	$ 30	$ 129	$ 58