Fair Value Measurements, Recurring (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2011 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2011 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2011 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2011 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Netting [Member]	Dec. 31, 2011 Netting [Member]	Sep. 30, 2012 Netting [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2011 Netting [Member] Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts			$ 164	$ 176	$ 3,351	$ 2,038	$ 105	$ 78	$ 0	$ 0			$ (3,292)	$ (1,940)
Physical purchase contracts			3	(2)	0	0	3	(2)	0	0			0	0
Investments of certain benefit plans			99	95	88	84	0	0	11	11			0	0
Foreign currency contracts			3		3		0		0				0
Other investments			0	0	0	0	0	0	0	0			0	0
Liabilities:
Commodity derivative contracts			16	25	3,191	1,864	117	101	0	0			(3,292)	(1,940)
Biofuels blending obligation			6		6		0		0				0
Foreign currency contracts			1	3	1	3	0	0	0	0			0	0
Fair Value Measurements (Textual)
Cash collateral deposits with brokers											213	136
Fair value asset transfers from Level 1 to Level 2	0	0
Fair value asset transfers from Level 2 to Level 1	$ 0	$ 0