Fair Value Measurements, Recurring (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	$ 89	$ 176
Physical purchase contracts	18	(2)
Investments of certain benefit plans	96	95
Other investments	0	0
Liabilities:
Commodity derivative contracts	8	25
Foreign currency contracts	5	3
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	2,781	2,038
Physical purchase contracts	0	0
Investments of certain benefit plans	85	84
Other investments	0	0
Liabilities:
Commodity derivative contracts	2,701	1,864
Foreign currency contracts	5	3
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	144	78
Physical purchase contracts	18	(2)
Investments of certain benefit plans	0	0
Other investments	0	0
Liabilities:
Commodity derivative contracts	143	101
Foreign currency contracts	0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	0	0
Physical purchase contracts	0	0
Investments of certain benefit plans	11	11
Other investments	0	0
Liabilities:
Commodity derivative contracts	0	0
Foreign currency contracts	0	0
Netting [Member]
Fair Value Measurements (Textual)
Cash received from brokers	81
Cash collateral deposits with brokers		136
Netting [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	(2,836)	(1,940)
Physical purchase contracts	0	0
Investments of certain benefit plans	0	0
Other investments	0	0
Liabilities:
Commodity derivative contracts	(2,836)	(1,940)
Foreign currency contracts	$ 0	$ 0