Fair Value Measurements, Recurring (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets:
Commodity derivative contracts	$ 1,371	$ 1,203
Foreign currency contracts		1
Investments of certain benefit plans	103	98
Total gross fair value, assets	1,474	1,313
Commodity derivative contracts, net assets	35	14
Net Carrying Value on Balance Sheet, Assets	138	124
Cash Collateral Received Not Offset	0	0
Liabilities:
Commodity derivative contracts	1,351	1,208
Biofuels blending obligation		10
Foreign currency contracts	5	1
Total gross fair value, liabilities	1,373	1,219
Commodity derivative contracts, net liabilities	8	6
Net Carrying Value on Balance Sheet, Liabilities	30	17
Cash Collateral Paid Not Offset	(79)	(114)
Physical Purchase Contracts [Member]
Assets:
Physical purchase contracts		11
Liabilities:
Physical purchase contracts	17
Fair Value, Inputs, Level 1 [Member]
Assets:
Commodity derivative contracts	1,345	1,143
Foreign currency contracts		1
Investments of certain benefit plans	92	87
Total gross fair value, assets	1,437	1,231
Liabilities:
Commodity derivative contracts	1,314	1,138
Biofuels blending obligation		0
Foreign currency contracts	5	1
Total gross fair value, liabilities	1,319	1,139
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Assets:
Physical purchase contracts		0
Liabilities:
Physical purchase contracts	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Commodity derivative contracts	26	60
Foreign currency contracts		0
Investments of certain benefit plans	0	0
Total gross fair value, assets	26	71
Liabilities:
Commodity derivative contracts	37	70
Biofuels blending obligation		10
Foreign currency contracts	0	0
Total gross fair value, liabilities	54	80
Fair Value, Inputs, Level 2 [Member] | Physical Purchase Contracts [Member]
Assets:
Physical purchase contracts		11
Liabilities:
Physical purchase contracts	17
Fair Value, Inputs, Level 3 [Member]
Assets:
Commodity derivative contracts	0	0
Foreign currency contracts		0
Investments of certain benefit plans	11	11
Total gross fair value, assets	11	11
Liabilities:
Commodity derivative contracts	0	0
Biofuels blending obligation		0
Foreign currency contracts	0	0
Total gross fair value, liabilities	0	0
Fair Value, Inputs, Level 3 [Member] | Physical Purchase Contracts [Member]
Assets:
Physical purchase contracts		0
Liabilities:
Physical purchase contracts	0
Netting [Member]
Assets:
Effect of Counterparty Netting	(1,331)	(1,189)
Effect of Cash Collateral Netting	(5)	0
Liabilities:
Effect of Counterparty Netting	(1,331)	(1,189)
Effect of Cash Collateral Netting	$ (12)	$ (13)