Condensed Consolidating Financial Information Statements of Cash Flows Tables (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	$ 656	$ 99
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(442)	(433)
Acquisitions of proved and unproved properties	(63)	(95)
Proceeds from divestitures of proved and unproved properties	319	892
Additions to other property and equipment	(3)	(3)
Other investing activities	142	19
Net Cash Provided By (Used In) Investing Activities	(47)	380
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	2,904	50
Payments on revolving credit facility borrowings	(3,485)	(50)
Cash paid to purchase debt	0	(982)
Cash paid for preferred stock dividends	(23)	(114)
Other financing activities	(6)	(16)
Intercompany advances, net	0	0
Net Cash Used In Financing Activities	(610)	(1,112)
Net decrease in cash and cash equivalents	(1)	(633)
Cash and cash equivalents, beginning of period	5	882
Cash and cash equivalents, end of period	4	249
Consolidation, eliminations [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	(4)	(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 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	(25)	12
Intercompany advances, net	0	0
Net Cash Used In Financing Activities	(25)	12
Net decrease in cash and cash equivalents	(29)	10
Cash and cash equivalents, beginning of period	(3)	(25)
Cash and cash equivalents, end of period	(32)	(15)
Parent Company [Member] | Reportable legal entities [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	78	1
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 Provided By (Used In) Investing Activities	0	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility borrowings	2,904	50
Payments on revolving credit facility borrowings	(3,485)	(50)
Cash paid to purchase debt		(982)
Cash paid for preferred stock dividends	(23)	(114)
Other financing activities	25	(24)
Intercompany advances, net	530	(476)
Net Cash Used In Financing Activities	(49)	(644)
Net decrease in cash and cash equivalents	29	(643)
Cash and cash equivalents, beginning of period	5	904
Cash and cash equivalents, end of period	34	261
Guarantor Subsidiaries [Member] | Reportable legal entities [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	577	96
CASH FLOWS FROM INVESTING ACTIVITIES:
Drilling and completion costs	(442)	(433)
Acquisitions of proved and unproved properties	(63)	(95)
Proceeds from divestitures of proved and unproved properties	319	892
Additions to other property and equipment	(3)	(3)
Other investing activities	142	19
Net Cash Provided By (Used In) Investing Activities	(47)	380
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	(2)	(1)
Intercompany advances, net	(528)	475
Net Cash Used In Financing Activities	(530)	(476)
Net decrease in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	1	2
Cash and cash equivalents, end of period	1	2
Non-Guarantor Subsidiaries [Member] | Reportable legal entities [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Cash Provided By Operating Activities	5	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 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	(4)	(3)
Intercompany advances, net	(2)	1
Net Cash Used In Financing Activities	(6)	(4)
Net decrease in cash and cash equivalents	(1)	0
Cash and cash equivalents, beginning of period	2	1
Cash and cash equivalents, end of period	$ 1	$ 1