Schedule of Cash Flow Hedge Instruments Gain Loss in Statement of Financial Performance (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	$ 179		$ 179
Derivative Instruments Reclassified From Accumulated Oci Into Stockholders Equity Effective Portion After Tax Ending Balance	193	115	193	115
AOCI
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) On Cash Flow Hedge (Effectiveness Portion) Total	4	121	4	338
Natural gas, oil and NGL sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	9	129	28	232
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	0	(5)	0	13
Gain (Loss) Recognized, Amount initially excluded from effectiveness testing	0	0	0	22
Gain (Loss) Recognized in Income, Commodity contracts	0	(5)	0	35
Commodity derivatives | AOCI
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI (Effective Portion)	0	122	0	372
Commodity derivatives | Natural gas, oil and NGL sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	9	129	28	270
Foreign currency derivatives | AOCI
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI (Effective Portion)	4	(1)	4	(34)
Foreign currency derivatives | Natural gas, oil and NGL sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	0	0	0	(20)
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	$ 0	$ 0	$ 0	$ (18)