Fair Value Measurements, Recurring (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets:
Commodity derivative contracts	$ 2,468	$ 3,132
Physical purchase contracts		1
Foreign currency contracts	3
Investments of certain benefit plans	102	108
Total gross fair value, assets	2,573	3,241
Effect of Counterparty Netting	(2,443)	(2,907)
Effect of Cash Collateral Netting	0	(99)
Commodity derivative contracts, net assets	25	126
Net Carrying Value on Balance Sheet, Assets	130	235
Cash Collateral Received Not Offset	0	0
Liabilities:
Commodity derivative contracts	2,489	2,920
Environmental credit obligations	43	14
Physical purchase contracts	4	5
Total gross fair value, liabilities	2,536	2,939
Effect of Counterparty Netting	(2,443)	(2,907)
Effect of Cash Collateral Netting	(46)	(13)
Commodity derivative contracts, net liabilities	0	0
Net Carrying Value on Balance Sheet, Liabilities	47	19
Cash Collateral Paid Not Offset	(155)	(25)
Fair Value, Inputs, Level 1 [Member]
Assets:
Commodity derivative contracts	2,438	3,096
Physical purchase contracts		0
Foreign currency contracts	3
Investments of certain benefit plans	91	97
Total gross fair value, assets	2,532	3,193
Liabilities:
Commodity derivative contracts	2,455	2,886
Environmental credit obligations	0	0
Physical purchase contracts	0	0
Total gross fair value, liabilities	2,455	2,886
Fair Value, Inputs, Level 2 [Member]
Assets:
Commodity derivative contracts	30	36
Physical purchase contracts		1
Foreign currency contracts	0
Investments of certain benefit plans	0	0
Total gross fair value, assets	30	37
Liabilities:
Commodity derivative contracts	34	34
Environmental credit obligations	43	14
Physical purchase contracts	4	5
Total gross fair value, liabilities	81	53
Fair Value, Inputs, Level 3 [Member]
Assets:
Commodity derivative contracts	0	0
Physical purchase contracts		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
Environmental credit obligations	0	0
Physical purchase contracts	0	0
Total gross fair value, liabilities	$ 0	$ 0