Fair Value Measurements (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Financial Assets:
Financial Assets: Natural Gas Options/Swaptions	$ 31	$ 100
Financial Assets: Crude Oil Swaps/Put Options	40	121
Financial Assets: Crude Oil Options/Swaptions		244
Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets [Abstract]
Net of Tax Impairment Charges for Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets	4,061
Pretax Impairment Charges for Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets	6,230
Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets Written Down During the Period - Fair value at End of Period	2,627
Proved Oil and Gas Properties, Other Property, Plant and Equipment and Other Assets Carrying Amount	8,857
Debt Disclosure [Abstract]
Estimated Fair Value of Debt	6,673	6,242
Aggregate Principal Amount of Current and Long-Term Debt	6,390	5,890
Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Financial Assets: Natural Gas Options/Swaptions	0	0
Financial Assets: Crude Oil Swaps/Put Options	0	0
Financial Assets: Crude Oil Options/Swaptions		0
Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Financial Assets: Natural Gas Options/Swaptions	31	100
Financial Assets: Crude Oil Swaps/Put Options	40	121
Financial Assets: Crude Oil Options/Swaptions		244
Fair Value, Inputs, Level 3 [Member]
Financial Assets:
Financial Assets: Natural Gas Options/Swaptions	0	0
Financial Assets: Crude Oil Swaps/Put Options	$ 0	0
Financial Assets: Crude Oil Options/Swaptions		$ 0