Fair Value Measurements, Recurring (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Assets:
Commodity derivative contracts	$ 248	$ 3,132
Physical purchase contracts	7	1
Foreign currency contracts	3
Investments of certain benefit plans	94	108
Total gross fair value, assets	352	3,241
Effect of Counterparty Netting	(203)	(2,907)
Effect of Cash Collateral Netting	0	(99)
Commodity derivative contracts, net assets	45	126
Net Carrying Value on Balance Sheet, Assets	149	235
Cash Collateral Received Not Offset	0	0
Liabilities:
Commodity derivative contracts	219	2,920
Environmental credit obligations	16	14
Physical purchase contracts	1	5
Foreign currency contracts	2
Total gross fair value, liabilities	238	2,939
Effect of Counterparty Netting	(203)	(2,907)
Effect of Cash Collateral Netting	(16)	(13)
Commodity derivative contracts, net liabilities	0	0
Net Carrying Value on Balance Sheet, Liabilities	19	19
Cash Collateral Paid Not Offset	(62)	(25)
Fair Value, Inputs, Level 1 [Member]
Assets:
Commodity derivative contracts	234	3,096
Physical purchase contracts	0	0
Foreign currency contracts	3
Investments of certain benefit plans	83	97
Total gross fair value, assets	320	3,193
Liabilities:
Commodity derivative contracts	207	2,886
Environmental credit obligations	0	0
Physical purchase contracts	0	0
Foreign currency contracts	2
Total gross fair value, liabilities	209	2,886
Fair Value, Inputs, Level 2 [Member]
Assets:
Commodity derivative contracts	14	36
Physical purchase contracts	7	1
Foreign currency contracts	0
Investments of certain benefit plans	0	0
Total gross fair value, assets	21	37
Liabilities:
Commodity derivative contracts	12	34
Environmental credit obligations	16	14
Physical purchase contracts	1	5
Foreign currency contracts	0
Total gross fair value, liabilities	29	53
Fair Value, Inputs, Level 3 [Member]
Assets:
Commodity derivative contracts	0	0
Physical purchase 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
Environmental credit obligations	0	0
Physical purchase contracts	0	0
Foreign currency contracts	0
Total gross fair value, liabilities	$ 0	$ 0