Natural Gas And Oil Properties (Details) $ in Millions	6 Months Ended
	Jun. 30, 2015 USD ($) $ / MMBTU $ / bbl	Jun. 30, 2014 USD ($) $ / MMBTU $ / bbl
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 | $	$ 60	$ 37
Impairment Of Oil And Gas Properties Net Of Tax | $	$ 944
Natural Gas [Member] | Henry Hub [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Full cost ceiling test, price | $ / MMBTU	3.39	4.10
Oil [Member] | West Texas Intermediate [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Full cost ceiling test, price	68.17	96.75
NGL [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Full cost ceiling test, price	12.53	43.31