Change in Accounting Principle - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018		Jun. 30, 2019		Jun. 30, 2018
Condensed Cash Flow Statements, Captions [Line Items]
NET INCOME (LOSS)	$ 98	$ (249)	[1]	$ 77	[1],[2]	$ (231)	[1],[2]
CASH FLOWS FROM OPERATING ACTIVITIES:
Depreciation, depletion and amortization	580	471	[3]	1,099		930	[2],[3]
Deferred income tax benefit				(314)		(9)	[2]
Derivative losses, net				30		368	[2]
Cash payments on derivative settlements, net				15		(55)	[2]
Stock-based compensation				17		18	[2]
Gains on sales of assets	(1)	(18)	[3]	(20)		(37)	[2],[3]
Impairments	1	54	[3]	2		64	[2],[3]
Exploration				25		73	[2]
(Gains) losses on investments				18		(139)	[2]
Other				41		(93)	[2]
Changes in assets and liabilities				(137)		62	[2]
Net Cash Provided By Operating Activities				853		951	[2]
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs				(1,070)		(928)	[2]
Business combination, net				(353)		0	[2]
Acquisitions of proved and unproved properties				(17)		(102)	[2]
Proceeds from divestitures of proved and unproved properties				82		384	[2]
Additions to other property and equipment				(18)		(5)	[2]
Proceeds from sales of other property and equipment				4		74	[2]
Proceeds from sales of investments				0		74	[2]
Net Cash Used In Investing Activities				(1,372)		(503)	[2]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings				6,416		6,118	[2]
Payments on revolving credit facility borrowings				(5,452)		(6,393)	[2]
Extinguishment of other financing				0		(122)	[2]
Cash paid to purchase debt				(381)		0	[2]
Cash paid for preferred stock dividends				(46)		(46)	[2]
Distributions to noncontrolling interest owners				(2)		(3)	[2]
Other				(16)		(4)	[2]
Net Cash Provided By (Used In) Financing Activities				519		(450)	[2]
Net decrease in cash and cash equivalents				0		(2)	[2]
Cash and cash equivalents, beginning of period				4		5	[2]
Cash and cash equivalents, end of period	4	3	[2]	4		3	[2]
Under Full Cost
Condensed Cash Flow Statements, Captions [Line Items]
NET INCOME (LOSS)	310	(16)		490		278
CASH FLOWS FROM OPERATING ACTIVITIES:
Depreciation, depletion and amortization	419	290		776		576
Deferred income tax benefit				(314)		(9)
Derivative losses, net				30		368
Cash payments on derivative settlements, net				15		(55)
Stock-based compensation				17		18
Gains on sales of assets	0	0		0		0
Impairments	1	46		2		46
Exploration				0		0
(Gains) losses on investments				18		(139)
Other				31		(86)
Changes in assets and liabilities				(107)		94
Net Cash Provided By Operating Activities				958		1,091
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs				(1,104)		(979)
Business combination, net				(353)
Acquisitions of proved and unproved properties				(88)		(191)
Proceeds from divestitures of proved and unproved properties				82		384
Additions to other property and equipment				(18)		(5)
Proceeds from sales of other property and equipment				4		74
Proceeds from sales of investments						74
Net Cash Used In Investing Activities				(1,477)		(643)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings				6,416		6,118
Payments on revolving credit facility borrowings				(5,452)		(6,393)
Extinguishment of other financing						(122)
Cash paid to purchase debt				(381)
Cash paid for preferred stock dividends				(46)		(46)
Distributions to noncontrolling interest owners				(2)		(3)
Other				(16)		(4)
Net Cash Provided By (Used In) Financing Activities				519		(450)
Net decrease in cash and cash equivalents				0		(2)
Cash and cash equivalents, beginning of period				4		5
Cash and cash equivalents, end of period	4	3		4		3
Successful Efforts Adjustment
Condensed Cash Flow Statements, Captions [Line Items]
NET INCOME (LOSS)	(212)	(233)		(413)		(509)
CASH FLOWS FROM OPERATING ACTIVITIES:
Depreciation, depletion and amortization	161	181		323		354
Deferred income tax benefit				0		0
Derivative losses, net				0		0
Cash payments on derivative settlements, net				0		0
Stock-based compensation				0		0
Gains on sales of assets	(1)	(18)		(20)		(37)
Impairments	0	8		0		18
Exploration				25		73
(Gains) losses on investments				0		0
Other				10		(7)
Changes in assets and liabilities				(30)		(32)
Net Cash Provided By Operating Activities				(105)		(140)
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs				34		51
Business combination, net				0
Acquisitions of proved and unproved properties				71		89
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				105		140
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings				0		0
Payments on revolving credit facility borrowings				0		0
Extinguishment of other financing						0
Cash paid to purchase debt				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 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.