Fair Value Measurements, Recurring (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Investments of certain benefit plans	$ 1,978	$ 1,909
Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	3,132	537
Physical purchase contracts	1
Investments of certain benefit plans	108	109
Total gross fair value, assets	3,241	646
Effect of Counterparty Netting	(2,907)	(505)
Effect of Cash Collateral Netting	(99)	(7)
Commodity derivative contracts, net assets	126	25
Net Carrying Value on Balance Sheet, Assets	235	134
Cash Collateral Received Not Offset	0	0
Liabilities:
Commodity derivative contracts	2,920	516
Biofuels blending obligation	14	11
Physical purchase contracts	5	5
Foreign currency contracts		8
Total gross fair value, liabilities	2,939	540
Effect of Counterparty Netting	(2,907)	(505)
Effect of Cash Collateral Netting	(13)	(6)
Commodity derivative contracts, net liabilities	0	5
Net Carrying Value on Balance Sheet, Liabilities	19	29
Cash Collateral Paid Not Offset	(25)	(76)
Fair Value, Inputs, Level 1 [Member]
Assets:
Investments of certain benefit plans	1,155	1,135
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	3,096	499
Physical purchase contracts	0
Investments of certain benefit plans	97	98
Total gross fair value, assets	3,193	597
Liabilities:
Commodity derivative contracts	2,886	492
Biofuels blending obligation	0	0
Physical purchase contracts	0	0
Foreign currency contracts		8
Total gross fair value, liabilities	2,886	500
Fair Value, Inputs, Level 2 [Member]
Assets:
Investments of certain benefit plans	823	774
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	36	38
Physical purchase contracts	1
Investments of certain benefit plans	0	0
Total gross fair value, assets	37	38
Liabilities:
Commodity derivative contracts	34	24
Biofuels blending obligation	14	11
Physical purchase contracts	5	5
Foreign currency contracts		0
Total gross fair value, liabilities	53	40
Fair Value, Inputs, Level 3 [Member]
Assets:
Investments of certain benefit plans	0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Commodity derivative contracts	0	0
Physical purchase 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	0
Physical purchase contracts	0	0
Foreign currency contracts		0
Total gross fair value, liabilities	$ 0	$ 0