Change in Accounting Principle - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
NET INCOME (LOSS)	$ (61)	$ (146)	[1],[2]	$ 16	$ (377)	[1],[2],[3]
ADJUSTMENTS TO RECONCILE NET INCOME (LOSS) TO CASH PROVIDED BY OPERATING ACTIVITIES:
Depreciation, depletion and amortization	573	405	[2]	1,672	1,335	[2],[3]
Deferred income tax benefit				(314)	(10)	[3]
Derivative (gains) losses, net				(137)	500	[3]
Cash receipts (payments) on derivative settlements, net				129	(162)	[3]
Stock-based compensation				24	25	[3]
Gains on sales of assets	(13)	10	[2]	(33)	(27)	[2],[3]
Impairments	9	58	[2]	11	122	[2],[3]
Exploration				35	81	[3]
(Gains) losses on investments				21	(139)	[3]
(Gains) losses on purchases or exchanges of debt				(70)	68
Other				42	(90)	[3]
Changes in assets and liabilities				(214)	69	[3]
Net Cash Provided By Operating Activities				1,182	1,395	[3]
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs				(1,640)	(1,407)	[3]
Business combination, net				(353)	0	[3]
Acquisitions of proved and unproved properties				(31)	(118)	[3]
Proceeds from divestitures of proved and unproved properties				110	395	[3]
Additions to other property and equipment				(27)	(11)	[3]
Proceeds from sales of other property and equipment				6	75	[3]
Proceeds from sales of investments				0	74	[3]
Net Cash Used In Investing Activities				(1,935)	(992)	[3]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings				8,805	9,095	[3]
Payments on revolving credit facility borrowings				(7,495)	(9,231)	[3]
Proceeds from issuance of senior notes, net				0	1,237	[3]
Cash paid to purchase debt				(457)	(1,285)	[3]
Extinguishment of other financing				0	(122)	[3]
Cash paid for preferred stock dividends				(69)	(69)	[3]
Distributions to noncontrolling interest owners				(2)	(5)	[3]
Other				(19)	(24)	[3]
Net Cash Provided By (Used In) Financing Activities				763	(404)	[3]
Net increase (decrease) in cash and cash equivalents				10	(1)	[3]
Cash and cash equivalents, beginning of period				4	5	[3]
Cash and cash equivalents, end of period	14	4	[3]	14	4	[3]
Under Full Cost
CASH FLOWS FROM OPERATING ACTIVITIES:
NET INCOME (LOSS)	144	85		634	363
ADJUSTMENTS TO RECONCILE NET INCOME (LOSS) TO CASH PROVIDED BY OPERATING ACTIVITIES:
Depreciation, depletion and amortization	421	291		1,197	867
Deferred income tax benefit				(314)	(10)
Derivative (gains) losses, net				(137)	500
Cash receipts (payments) on derivative settlements, net				129	(162)
Stock-based compensation				24	25
Gains on sales of assets	0	0		0	0
Impairments	1	5		3	51
Exploration				0	0
(Gains) losses on investments				21	(139)
(Gains) losses on purchases or exchanges of debt				(70)	68
Other				33	(83)
Changes in assets and liabilities				(169)	116
Net Cash Provided By Operating Activities				1,351	1,596
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs				(1,694)	(1,482)
Business combination, net				(353)
Acquisitions of proved and unproved properties				(146)	(244)
Proceeds from divestitures of proved and unproved properties				110	395
Additions to other property and equipment				(27)	(11)
Proceeds from sales of other property and equipment				6	75
Proceeds from sales of investments					74
Net Cash Used In Investing Activities				(2,104)	(1,193)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings				8,805	9,095
Payments on revolving credit facility borrowings				(7,495)	(9,231)
Proceeds from issuance of senior notes, net					1,237
Cash paid to purchase debt				(457)	(1,285)
Extinguishment of other financing					(122)
Cash paid for preferred stock dividends				(69)	(69)
Distributions to noncontrolling interest owners				(2)	(5)
Other				(19)	(24)
Net Cash Provided By (Used In) Financing Activities				763	(404)
Net increase (decrease) in cash and cash equivalents				10	(1)
Cash and cash equivalents, beginning of period				4	5
Cash and cash equivalents, end of period	14	4		14	4
Successful Efforts Adjustment
CASH FLOWS FROM OPERATING ACTIVITIES:
NET INCOME (LOSS)	(205)	(231)		(618)	(740)
ADJUSTMENTS TO RECONCILE NET INCOME (LOSS) TO CASH PROVIDED BY OPERATING ACTIVITIES:
Depreciation, depletion and amortization	152	114		475	468
Deferred income tax benefit				0	0
Derivative (gains) losses, net				0	0
Cash receipts (payments) on derivative settlements, net				0	0
Stock-based compensation				0	0
Gains on sales of assets	(13)	10		(33)	(27)
Impairments	8	53		8	71
Exploration				35	81
(Gains) losses on investments				0	0
(Gains) losses on purchases or exchanges of debt				0	0
Other				9	(7)
Changes in assets and liabilities				(45)	(47)
Net Cash Provided By Operating Activities				(169)	(201)
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs				54	75
Business combination, net				0
Acquisitions of proved and unproved properties				115	126
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 Used In Investing Activities				169	201
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings				0	0
Payments on revolving credit facility borrowings				0	0
Proceeds from issuance of senior notes, net					0
Cash paid to purchase debt				0	0
Extinguishment of other financing					0
Cash paid for preferred stock dividends				0	0
Distributions to noncontrolling interest owners				0	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		$ 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.