Schedule of Cash Flow Hedge Instruments Gain Loss in Statement of Financial Performance (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Aoci
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedge (Effectiveness Portion) Total	$ (5)	$ 220		$ 217
Natural Gas And Oil Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	17	29	19	103
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)		8		18
Gain (Loss) Recognized, Amount initially excluded from effectiveness testing				22
Gain (Loss) Recognized in Income, Commodity contracts		8		40
Commodity derivatives | Aoci
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI (Effective Portion)		234		250
Commodity derivatives | Natural Gas And Oil Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	17	67	19	141
Foreign currency derivatives | Aoci
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI (Effective Portion)	(5)	(14)		(33)
Foreign currency derivatives | Natural Gas And Oil Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)		(20)		(20)
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)		$ (18)		$ (18)