Condensed Consolidating Financial Information - Information Statements of Cash Flows Tables (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Sep. 30, 2017	[1]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	$ 456	$ 588	[1]
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(515)	(420)	[1]
Business combination, net	(353)	0	[1]
Acquisitions of proved and unproved properties	(6)	(17)	[1]
Proceeds from divestitures of proved and unproved properties	26	319	[1]
Additions to other property and equipment	(9)	(3)	[1]
Other investing activities	1	142
Net Cash Provided By (Used In) Investing Activities	(856)	21	[1]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	3,572	2,904	[1]
Payments on revolving credit facility borrowings	(3,136)	(3,485)	[1]
Cash paid to purchase debt	(1)			$ 0
Cash paid for preferred stock dividends	(23)	(23)	[1]
Other financing activities	(8)	(6)
Intercompany advances, net	0	0
Net Cash Provided By (Used In) Financing Activities	404	(610)	[1]
Net increase (decrease) in cash and cash equivalents	4	(1)	[1]
Cash and cash equivalents, beginning of period	4	5	[1]
Cash and cash equivalents, end of period	8	4	[1]
Eliminations
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	(1)	(4)
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	0	0
Business combination, net	0
Acquisitions of proved and unproved properties	0	0
Proceeds from divestitures of proved and unproved properties	0	0
Additions to other property and equipment	0	0
Other investing activities	0	0
Net Cash Provided By (Used In) Investing Activities	0	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	0	0
Payments on revolving credit facility borrowings	0	0
Cash paid to purchase debt	0
Cash paid for preferred stock dividends	0	0
Other financing activities	1	(25)
Intercompany advances, net	0	0
Net Cash Provided By (Used In) Financing Activities	1	(25)
Net increase (decrease) in cash and cash equivalents	0	(29)
Cash and cash equivalents, beginning of period	(2)	(3)
Cash and cash equivalents, end of period	(2)	(32)
Parent | Reportable legal entities
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	0	78
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	0	0
Business combination, net	0
Acquisitions of proved and unproved properties	0	0
Proceeds from divestitures of proved and unproved properties	0	0
Additions to other property and equipment	0	0
Other investing activities	0	0
Net Cash Provided By (Used In) Investing Activities	0	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	3,449	2,904
Payments on revolving credit facility borrowings	(3,026)	(3,485)
Cash paid to purchase debt	(1)
Cash paid for preferred stock dividends	(23)	(23)
Other financing activities	(7)	25
Intercompany advances, net	(393)	530
Net Cash Provided By (Used In) Financing Activities	(1)	(49)
Net increase (decrease) in cash and cash equivalents	(1)	29
Cash and cash equivalents, beginning of period	4	5
Cash and cash equivalents, end of period	3	34
Guarantor Subsidiaries | Reportable legal entities
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	421	509
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(406)	(420)
Business combination, net	(381)
Acquisitions of proved and unproved properties	(6)	(17)
Proceeds from divestitures of proved and unproved properties	26	319
Additions to other property and equipment	(6)	(3)
Other investing activities	1	142
Net Cash Provided By (Used In) Investing Activities	(772)	21
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	0	0
Payments on revolving credit facility borrowings	0	0
Cash paid to purchase debt	0
Cash paid for preferred stock dividends	0	0
Other financing activities	(1)	(2)
Intercompany advances, net	352	(528)
Net Cash Provided By (Used In) Financing Activities	351	(530)
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	1	1
Cash and cash equivalents, end of period	1	1
Non-Guarantor Subsidiaries | Reportable legal entities
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	36	5
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(109)	0
Business combination, net	28
Acquisitions of proved and unproved properties	0	0
Proceeds from divestitures of proved and unproved properties	0	0
Additions to other property and equipment	(3)	0
Other investing activities	0	0
Net Cash Provided By (Used In) Investing Activities	(84)	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	123	0
Payments on revolving credit facility borrowings	(110)	0
Cash paid to purchase debt	0
Cash paid for preferred stock dividends	0	0
Other financing activities	(1)	(4)
Intercompany advances, net	41	(2)
Net Cash Provided By (Used In) Financing Activities	53	(6)
Net increase (decrease) in cash and cash equivalents	5	(1)
Cash and cash equivalents, beginning of period	1	2
Cash and cash equivalents, end of period	$ 6	$ 1

[1] Financial information for 2018 has been recast to reflect the retrospective application of the successful efforts method of accounting. See Note 1.