Fair Value Measurements, Recurring (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Assets:
Investments of certain benefit plans	$ 71	$ 69
Total gross fair value, assets	972	984
Effect of Counterparty Netting	(882)	(875)
Effect of Cash Collateral Netting	(11)	0
Net Carrying Value on Balance Sheet, Assets	79	109
Liabilities:
Environmental credit obligations	231	188
Total gross fair value, liabilities	1,230	1,088
Effect of Counterparty Netting	(882)	(875)
Effect of Cash Collateral Netting	(108)	(20)
Net Carrying Value on Balance Sheet, Liabilities	240	193
Commodity Contracts [Member]
Assets:
Derivative contracts	895	912
Effect of Counterparty Netting	(882)	(875)
Effect of Cash Collateral Netting	(11)	0
Derivative contracts, net assets	2	37
Cash Collateral Received Not Offset	0	0
Liabilities:
Derivative contracts	990	895
Effect of Counterparty Netting	(882)	(875)
Effect of Cash Collateral Netting	(108)	(20)
Derivative contracts, net liabilities	0	0
Cash Collateral Paid Not Offset	(171)	(88)
Foreign Currency Contracts [Member]
Assets:
Derivative contracts	6	3
Derivative contracts, net assets	6	3
Liabilities:
Derivative contracts	1
Derivative contracts, net liabilities	1
Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	8	5
Derivative contracts, net liabilities	8	5
Fair Value, Inputs, Level 1 [Member]
Assets:
Investments of certain benefit plans	63	58
Total gross fair value, assets	930	935
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	975	872
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	861	874
Liabilities:
Derivative contracts	974	872
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	6	3
Liabilities:
Derivative contracts	1
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Investments of certain benefit plans	0	0
Total gross fair value, assets	34	38
Liabilities:
Environmental credit obligations	231	188
Total gross fair value, liabilities	255	216
Fair Value, Inputs, Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	34	38
Liabilities:
Derivative contracts	16	23
Fair Value, Inputs, Level 2 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	0	0
Liabilities:
Derivative contracts	0
Fair Value, Inputs, Level 2 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	8	5
Fair Value, Inputs, Level 3 [Member]
Assets:
Investments of certain benefit plans	8	11
Total gross fair value, assets	8	11
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	0	0
Fair Value, Inputs, Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	0	0
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 3 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	0	0
Liabilities:
Derivative contracts	0
Fair Value, Inputs, Level 3 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	$ 0	$ 0