Supplemental Oil And Gas Disclosures (Narrative) (Details) ft³ in Thousands, $ in Millions	12 Months Ended			120 Months Ended	156 Months Ended
	Dec. 31, 2016 USD ($) $ / bbl $ / MMBTU site ft³	Dec. 31, 2015 USD ($) $ / bbl $ / MMBTU site ft³	Dec. 31, 2014 USD ($) a $ / bbl $ / MMBTU site ft³	Dec. 31, 2013 USD ($) ft³	Dec. 31, 2016 USD ($) site ft³	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)
Natural Gas and Oil Properties [Line Items]
Natural gas, oil and NGL reserves discount	10.00%	10.00%	10.00%
Period of time needed to calculate ceiling value of reserves	12 months	12 months	12 months
Cash flow hedges impact on ceiling value, net of tax | $									$ 40	$ 60
Net unevaluated costs excluded from amortization | $	$ 147	$ 332	$ 1,535	$ 91	$ 2,105
Impairment of natural gas and oil properties, net of tax | $						$ 506	$ 297	$ 641	$ 1,746	$ 944
Percentage of present worth of proved reserves evaluated in audit	99.00%	100.00%	97.00%
Capitalized interest based on weighted average cost of borrowings | $	$ 152	$ 204	$ 55
Capitalized internal costs related to acquisition, exploration and development | $	112	307	320
Capitalized internal costs related to acquisition, exploration and development activities - subsidiaries | $	$ 19	$ 118	$ 123
Proved developed and undeveloped reserves	5,253,000,000	6,215,000,000	10,747,000,000	6,976,000,000	5,253,000,000
Production	875,000,000	976,000,000	768,000,000
Production volumes replaced with proved reserve additions, net upward revisions and acquisitions, percentage			550.00%
Extensions, discoveries and other additions	282,000,000	592,000,000	1,693,000,000
Net revisions	(354,000,000)	(4,083,000,000)	543,000,000
Undeveloped Properties Marcellus Shale [Member]
Natural Gas and Oil Properties [Line Items]
Net unevaluated costs excluded from amortization | $	$ 94
Undeveloped Properties New Ventures - Excluding Canada [Member]
Natural Gas and Oil Properties [Line Items]
Net unevaluated costs excluded from amortization | $	100
Wells In Progress [Member]
Natural Gas and Oil Properties [Line Items]
Net unevaluated costs excluded from amortization | $	$ 113
Southwest Appalachia [Member]
Natural Gas and Oil Properties [Line Items]
Proved developed and undeveloped reserves	677,000,000	611,000,000	2,297,000,000		677,000,000
Production	148,000,000	143,000,000	3,000,000
Extensions, discoveries and other additions	157,000,000	88,000,000
Net revisions	72,000,000	(1,666,000,000)
Other Properties [Member]
Natural Gas and Oil Properties [Line Items]
Proved developed and undeveloped reserves	5,000,000	4,000,000	190,000,000	218,000,000	5,000,000
Production	2,000,000	8,000,000	17,000,000
Extensions, discoveries and other additions		1,000,000	2,000,000
Net revisions	3,000,000	1,000,000	(15,000,000)
Undeveloped Properties, Various Locations [Member]
Natural Gas and Oil Properties [Line Items]
Natural gas, oil and NGL reserves discount	10.00%	10.00%	10.00%
Proved undeveloped reserves	77,000,000	217,000,000	181,000,000		77,000,000
Number of locations | site	15	75	60		15
Present value of proved reserves, discounted basis | $	$ (11)	$ (34)	$ (28)		$ (11)
Proved reserves, committed development period	5 years
Chesapeake and Statoil Property Acquisitions [Member]
Natural Gas and Oil Properties [Line Items]
Net unevaluated costs excluded from amortization | $	$ 1,600
Chesapeake Property Acquisition [Member]
Natural Gas and Oil Properties [Line Items]
Area of land purchased | a			413,000
Chesapeake Property Acquisition [Member] | Southwest Appalachia [Member]
Natural Gas and Oil Properties [Line Items]
Area of land purchased | a			413,000
Natural Gas [Member]
Natural Gas and Oil Properties [Line Items]
Average market prices used in reserves | $ / MMBTU	2.48	2.59	4.35
Oil [Member]
Natural Gas and Oil Properties [Line Items]
Average market prices used in reserves | $ / bbl	39.25	46.79	91.48
NGL [Member]
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price | $ / bbl	6.74	6.82	23.79
Impairment of natural gas and oil properties, net of tax | $		$ 1,586
Average market prices used in reserves | $ / MMBTU	6.74	6.82	23.79
Natural Gas and Oil [Member]
Natural Gas and Oil Properties [Line Items]
Proved developed and undeveloped reserves	5,253,000,000	6,215,000,000			5,253,000,000
Synthetic Gas, Synthetic Oil or Nonrenewable Natural Resources [Member]
Natural Gas and Oil Properties [Line Items]
Proved developed and undeveloped reserves	0				0