Acquisitions And Divestitures (Narrative) (Details) ft³ in Millions, $ in Millions		1 Months Ended							3 Months Ended								12 Months Ended
	Dec. 19, 2014 USD ($)	Sep. 30, 2016 USD ($) a	Jul. 31, 2016 USD ($)	Nov. 30, 2015 USD ($)	May 31, 2015 USD ($)	Apr. 30, 2015 USD ($) mi ft³	Jan. 31, 2015 USD ($) a	Dec. 31, 2014 USD ($) a ft³	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) a	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) a item ft³
Business Acquisition [Line Items]
Payments on long-term debt																	$ 1,175	$ 500
Capital spending																	593	1,798	$ 2,043
Repayment of short-term debt																		4,500
General and administrative expenses																	247	246	221
Interest expense																	88	56	59
Other current assets									$ 35				$ 48				35	48
Revenues									684	$ 651	$ 522	$ 579	687	$ 749	$ 764	$ 933	2,436	3,133	4,038
Operating income (loss)									122	$ (725)	$ (492)	$ (1,100)	(2,561)	$ (2,842)	$ (1,284)	$ 165	$ (2,195)	(6,522)	1,373
Bridge Loan [Member]
Business Acquisition [Line Items]
Bridge loan	$ 4,500							$ 4,500					4,500					$ 4,500	$ 4,500
Debt instrument, term	364 days																	364 days	364 days
Repayment of short-term debt							$ 4,500
Debt issuance costs							$ 47
Unsecured Debt [Member] | Term Loan due December 2016 [Member]
Business Acquisition [Line Items]
Loans payable								$ 500					$ 500					$ 500	$ 500
Maturity date, year and month																		2016-12
Debt instrument, term																			2 years
Long-term Debt [Member] | Term Loan 1 due December 2020 [Member]
Business Acquisition [Line Items]
Payments on long-term debt		$ 48	$ 375
Loans payable				$ 750
Maturity date, year and month																	2020-12	2018-11
Debt instrument, term				3 years
Debt issuance costs									$ 3								$ 3
WPX Property Acquisition [Member]
Business Acquisition [Line Items]
Area of land purchased | a							46,700
Cash consideration							$ 270
Net production per day of acreage sold in MMcf | ft³								50											50
Number of horizontal wells operated | item																			63
Firm transportation capacity assumed, per day | ft³																			260
Firm transportation, useful life																			19 years
Amortization																	$ 17	$ 8
Percentage of interest acquired													86.00%					86.00%
Assets acquired and liabilities net book value							$ 270
Statoil Property Acquisition [Member]
Business Acquisition [Line Items]
Area of land purchased | a							30,000
Percentage of interest acquired							20.00%
Allocated to natural gas and oil properties							$ 357
Chesapeake Property Acquisition [Member]
Business Acquisition [Line Items]
Area of land purchased | a								413,000											413,000
Cash consideration								$ 4,949
Assets acquired and liabilities net book value								4,949											$ 4,949
General and administrative expenses																			1
Interest expense																			5
Revenues																			10
Operating income (loss)																			2
Chesapeake Property Acquisition [Member] | Bridge Loan [Member]
Business Acquisition [Line Items]
Other current assets								47											47
Chesapeake Property Acquisition [Member] | Unsecured Debt [Member] | Term Loan due December 2016 [Member]
Business Acquisition [Line Items]
Unamortized fees								$ 1											$ 1
West Virginia [Member]
Business Acquisition [Line Items]
Area of land sold | a		55,000								55,000
Proceeds from sale of oil and gas property and equipment		$ 422
East Texas and Arkoma Basin [Member]
Business Acquisition [Line Items]
Proceeds from sale of oil and gas property and equipment					$ 211
Reduction in capitalized costs relating to proceeds					$ 205
Bradford And Lycoming Counties, Pennsylvania [Member]
Business Acquisition [Line Items]
Proceeds from sale of oil and gas property and equipment						$ 489
Net book value						206
Gain on sale of property						$ 283
Number of miles of natural gas gathering pipeline | mi						100
Pipeline capacity per day | ft³						600