Natural Gas And Oil Properties (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / MMBTU $ / bbl	Sep. 30, 2014 USD ($) $ / MMBTU $ / bbl	Jun. 30, 2015 USD ($)
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Discount rate of natural gas and oil reserves	10.00%
Cash flow hedges impact on ceiling value, net of tax	$ 40	$ 14
Impairment of natural gas and oil properties, net of tax	$ 1,746		$ 944
Natural Gas [Member] | Henry Hub [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Full cost ceiling test, price | $ / MMBTU	3.06	4.24
Oil [Member] | West Texas Intermediate [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Full cost ceiling test, price | $ / bbl	55.73	95.56
NGL [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Full cost ceiling test, price | $ / bbl	8.62	36.70