Fair Value Measurements, Recurring (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Assets:
Investments of certain benefit plans	$ 70	$ 69
Total gross fair value, assets	732	984
Effect of Counterparty Netting	(612)	(875)
Effect of Cash Collateral Netting	(5)	0
Net Carrying Value on Balance Sheet, Assets	115	109
Liabilities:
Environmental credit obligations	274	188
Total gross fair value, liabilities	907	1,088
Effect of Counterparty Netting	(612)	(875)
Effect of Cash Collateral Netting	(7)	(20)
Net Carrying Value on Balance Sheet, Liabilities	288	193
Commodity Contracts [Member]
Assets:
Derivative contracts	662	912
Effect of Counterparty Netting	(612)	(875)
Effect of Cash Collateral Netting	(5)	0
Derivative contracts, net assets	45	37
Cash Collateral Received Not Offset	0	0
Liabilities:
Derivative contracts	619	895
Effect of Counterparty Netting	(612)	(875)
Effect of Cash Collateral Netting	(7)	(20)
Derivative contracts, net liabilities	0	0
Cash Collateral Paid Not Offset	(68)	(88)
Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	4	5
Derivative contracts, net liabilities	4	5
Foreign Currency Contracts [Member]
Assets:
Derivative contracts		3
Derivative contracts, net assets		3
Liabilities:
Derivative contracts	10
Derivative contracts, net liabilities	10
Fair Value, Inputs, Level 1 [Member]
Assets:
Investments of certain benefit plans	59	58
Total gross fair value, assets	709	935
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	615	872
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	650	874
Liabilities:
Derivative contracts	605	872
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts		3
Liabilities:
Derivative contracts	10
Fair Value, Inputs, Level 2 [Member]
Assets:
Investments of certain benefit plans	0	0
Total gross fair value, assets	12	38
Liabilities:
Environmental credit obligations	274	188
Total gross fair value, liabilities	292	216
Fair Value, Inputs, Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	12	38
Liabilities:
Derivative contracts	14	23
Fair Value, Inputs, Level 2 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	4	5
Fair Value, Inputs, Level 2 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts		0
Liabilities:
Derivative contracts	0
Fair Value, Inputs, Level 3 [Member]
Assets:
Investments of certain benefit plans	11	11
Total gross fair value, assets	11	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] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 3 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts		$ 0
Liabilities:
Derivative contracts	$ 0