Change in Accounting Principle - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Sep. 30, 2017	[1]
Condensed Cash Flow Statements, Captions [Line Items]
NET INCOME (LOSS)	$ (21)	$ 18	[1],[2]
CASH FLOWS FROM OPERATING ACTIVITIES:
Depreciation, depletion and amortization	519	459	[1],[3]
Deferred income tax benefit	(314)	0	[1]
Derivative losses, net	304	117	[1]
Cash receipts on derivative settlements, net	14	13	[1]
Stock-based compensation	6	9	[1]
Gains on sales of assets	(19)	(19)	[1],[3]
Impairments	1	10	[1],[3]
Exploration	18	68	[1]
(Gains) losses on investments	1	(139)	[1]
Other	40	(36)	[1]
Changes in assets and liabilities	(93)	88	[1]
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]
Proceeds from sales of other property and equipment	1	68	[1]
Proceeds from sales of investments	0	74	[1]
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]
Distributions to noncontrolling interest owners	0	(2)	[1]
Other	(8)	(4)	[1]
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]
Under Full Cost
Condensed Cash Flow Statements, Captions [Line Items]
NET INCOME (LOSS)	180	294
CASH FLOWS FROM OPERATING ACTIVITIES:
Depreciation, depletion and amortization	357	286
Deferred income tax benefit	(314)
Derivative losses, net	304	117
Cash receipts on derivative settlements, net	14	13
Stock-based compensation	6	9
Gains on sales of assets	0	0
Impairments	1	0
Exploration	0	0
(Gains) losses on investments	1	(139)
Other	31	(28)
Changes in assets and liabilities	(78)	104
Net Cash Provided By Operating Activities	502	656
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(533)	(442)
Business combination, net	(353)
Acquisitions of proved and unproved properties	(34)	(63)
Proceeds from divestitures of proved and unproved properties	26	319
Additions to other property and equipment	(9)	(3)
Proceeds from sales of other property and equipment	1	68
Proceeds from sales of investments		74
Net Cash Provided By (Used In) Investing Activities	(902)	(47)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	3,572	2,904
Payments on revolving credit facility borrowings	(3,136)	(3,485)
Cash paid to purchase debt	(1)
Cash paid for preferred stock dividends	(23)	(23)
Distributions to noncontrolling interest owners		(2)
Other	(8)	(4)
Net Cash Provided By (Used In) Financing Activities	404	(610)
Net increase (decrease) in cash and cash equivalents	4	(1)
Cash and cash equivalents, beginning of period	4	5
Cash and cash equivalents, end of period	8	4
Successful Efforts Adjustment
Condensed Cash Flow Statements, Captions [Line Items]
NET INCOME (LOSS)	(201)	(276)
CASH FLOWS FROM OPERATING ACTIVITIES:
Depreciation, depletion and amortization	162	173
Deferred income tax benefit	0
Derivative losses, net	0	0
Cash receipts on derivative settlements, net	0	0
Stock-based compensation	0	0
Gains on sales of assets	(19)	(19)
Impairments	0	10
Exploration	18	68
(Gains) losses on investments	0	0
Other	9	(8)
Changes in assets and liabilities	(15)	(16)
Net Cash Provided By Operating Activities	(46)	(68)
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	18	22
Business combination, net	0
Acquisitions of proved and unproved properties	28	46
Proceeds from divestitures of proved and unproved properties	0	0
Additions to other property and equipment	0	0
Proceeds from sales of other property and equipment	0	0
Proceeds from sales of investments		0
Net Cash Provided By (Used In) Investing Activities	46	68
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
Distributions to noncontrolling interest owners		0
Other	0	0
Net Cash Provided By (Used In) Financing Activities	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	$ 0	$ 0

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

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

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