Condensed Consolidating Financial Information Condensed Consolidating Financial Information Statements of Cash Flows Tables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided By (Used In) Operating Activities	$ 745	$ (204)	$ 1,234
Drilling and completion costs	(2,186)	(1,295)	(3,095)
Acquisitions of proved and unproved properties	(285)	(788)	(533)
Proceeds from divestitures of proved and unproved properties	1,249	1,406	189
Additions to other property and equipment	(21)	(37)	(143)
Other Investing Activities Intercompany	55
Net Cash Used In Investing Activities	(1,188)	(660)	(3,451)
Proceeds from revolving credit facility borrowings	7,771	5,146	0
Payments on revolving credit facility borrowings	(6,990)	(5,146)	0
Proceeds from issuance of senior notes, net	1,585	2,210	0
Proceeds from issuance of term loan, net	0	1,476	0
Cash paid to purchase debt	(2,592)	(2,734)	(508)
Cash paid for preferred stock dividends	(183)	0	(171)
Other Financing Activities Intercompany	(25)
Payments for Repurchase of Redeemable Noncontrolling Interest	0	0	143
Intercompany advances, net	0
Net Cash Provided By (Used In) Financing Activities	(434)	921	(1,066)
Net increase (decrease) in cash and cash equivalents	(877)	57	(3,283)
Cash and cash equivalents, beginning of period	882	825	4,108
Cash and cash equivalents, end of period	5	882	$ 825
Consolidation, Eliminations [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided By (Used In) Operating Activities	(10)
Drilling and completion costs	0
Acquisitions of proved and unproved properties	0
Proceeds from divestitures of proved and unproved properties	0
Additions to other property and equipment	0
Other Investing Activities Intercompany	0
Net Cash Used In Investing Activities	0
Proceeds from revolving credit facility borrowings	0
Payments on revolving credit facility borrowings	0
Proceeds from issuance of senior notes, net	0
Cash paid to purchase debt	0
Cash paid for preferred stock dividends	0
Other Financing Activities Intercompany	32
Intercompany advances, net	0
Net Cash Provided By (Used In) Financing Activities	32
Net increase (decrease) in cash and cash equivalents	22
Cash and cash equivalents, beginning of period	(25)
Cash and cash equivalents, end of period	(3)	(25)
Parent Company [Member] | Reportable Legal Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided By (Used In) Operating Activities	5
Drilling and completion costs	0
Acquisitions of proved and unproved properties	0
Proceeds from divestitures of proved and unproved properties	0
Additions to other property and equipment	0
Other Investing Activities Intercompany	0
Net Cash Used In Investing Activities	0
Proceeds from revolving credit facility borrowings	7,771
Payments on revolving credit facility borrowings	(6,990)
Proceeds from issuance of senior notes, net	1,585
Cash paid to purchase debt	(2,592)
Cash paid for preferred stock dividends	(183)
Other Financing Activities Intercompany	(39)
Intercompany advances, net	456
Net Cash Provided By (Used In) Financing Activities	(904)
Net increase (decrease) in cash and cash equivalents	(899)
Cash and cash equivalents, beginning of period	904
Cash and cash equivalents, end of period	5	904
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided By (Used In) Operating Activities	736
Drilling and completion costs	(2,186)
Acquisitions of proved and unproved properties	(285)
Proceeds from divestitures of proved and unproved properties	1,249
Additions to other property and equipment	(21)
Other Investing Activities Intercompany	55
Net Cash Used In Investing Activities	(1,188)
Proceeds from revolving credit facility borrowings	0
Payments on revolving credit facility borrowings	0
Proceeds from issuance of senior notes, net	0
Cash paid to purchase debt	0
Cash paid for preferred stock dividends	0
Other Financing Activities Intercompany	(5)
Intercompany advances, net	(456)
Net Cash Provided By (Used In) Financing Activities	451
Net increase (decrease) in cash and cash equivalents	(1)
Cash and cash equivalents, beginning of period	2
Cash and cash equivalents, end of period	1	2
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided By (Used In) Operating Activities	14
Drilling and completion costs	0
Acquisitions of proved and unproved properties	0
Proceeds from divestitures of proved and unproved properties	0
Additions to other property and equipment	0
Other Investing Activities Intercompany	0
Net Cash Used In Investing Activities	0
Proceeds from revolving credit facility borrowings	0
Payments on revolving credit facility borrowings	0
Proceeds from issuance of senior notes, net	0
Cash paid to purchase debt	0
Cash paid for preferred stock dividends	0
Other Financing Activities Intercompany	(13)
Intercompany advances, net	0
Net Cash Provided By (Used In) Financing Activities	(13)
Net increase (decrease) in cash and cash equivalents	1
Cash and cash equivalents, beginning of period	1
Cash and cash equivalents, end of period	$ 2	$ 1