Condensed Consolidating Financial Information Statements of Cash Flows Tables (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	$ 1,091	$ (58)
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(979)	(1,031)
Acquisitions of proved and unproved properties	(191)	(162)
Proceeds from divestitures of proved and unproved properties	384	951
Additions to other property and equipment	(5)	(7)
Other investing activities	148	26
Net Cash Used In Investing Activities	(643)	(223)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	6,118	2,551
Payments on revolving credit facility borrowings	(6,393)	(1,976)
Proceeds from issuance of senior notes, net	0	742
Cash paid to purchase debt	0	(1,746)
Cash paid for preferred stock dividends	(46)	(137)
Other financing activities	(129)	(22)
Intercompany advances, net	0	0
Net Cash Used In Financing Activities	(450)	(588)
Net decrease in cash and cash equivalents	(2)	(869)
Cash and cash equivalents, beginning of period	5	882
Cash and cash equivalents, end of period	3	13
Eliminations [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	(8)	(4)
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	0	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 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
Proceeds from issuance of senior notes, net		0
Cash paid to purchase debt		0
Cash paid for preferred stock dividends	0	0
Other financing activities	6	25
Intercompany advances, net	0	0
Net Cash Used In Financing Activities	6	25
Net decrease in cash and cash equivalents	(2)	21
Cash and cash equivalents, beginning of period	(3)	(25)
Cash and cash equivalents, end of period	(5)	(4)
Parent Company [Member] | Reportable legal entities [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	88	2
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	0	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 Used In Investing Activities	0	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	6,118	2,551
Payments on revolving credit facility borrowings	(6,393)	(1,976)
Proceeds from issuance of senior notes, net		742
Cash paid to purchase debt		(1,746)
Cash paid for preferred stock dividends	(46)	(137)
Other financing activities	(2)	(38)
Intercompany advances, net		(287)
Intercompany advances, net	235
Net Cash Used In Financing Activities	(88)	(891)
Net decrease in cash and cash equivalents	0	(889)
Cash and cash equivalents, beginning of period	5	904
Cash and cash equivalents, end of period	5	15
Guarantor Subsidiaries [Member] | Reportable legal entities [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	1,006	(64)
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(979)	(1,031)
Acquisitions of proved and unproved properties	(191)	(162)
Proceeds from divestitures of proved and unproved properties	384	951
Additions to other property and equipment	(5)	(7)
Other investing activities	148	26
Net Cash Used In Investing Activities	(643)	(223)
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
Cash paid for preferred stock dividends	0	0
Other financing activities	(126)	(2)
Intercompany advances, net	(237)
Intercompany advances, net		288
Net Cash Used In Financing Activities	(363)	286
Net decrease in cash and cash equivalents	0	(1)
Cash and cash equivalents, beginning of period	1	2
Cash and cash equivalents, end of period	1	1
Non-Guarantor Subsidiaries [Member] | Reportable legal entities [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	5	8
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	0	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 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
Proceeds from issuance of senior notes, net		0
Cash paid to purchase debt		0
Cash paid for preferred stock dividends	0	0
Other financing activities	(7)	(7)
Intercompany advances, net		(1)
Intercompany advances, net	2
Net Cash Used In Financing Activities	(5)	(8)
Net decrease in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	2	1
Cash and cash equivalents, end of period	$ 2	$ 1