Fair Value Measurements, Recurring (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Assets:
Investments of certain benefit plans	$ 68	$ 75
Total gross fair value, assets	848	760
Effect of Counterparty Netting	(706)	(557)
Effect of Cash Collateral Netting	0	(12)
Net Carrying Value on Balance Sheet, Assets	142	191
Liabilities:
Environmental credit obligations	63	2
Total gross fair value, liabilities	798	565
Effect of Counterparty Netting	(706)	(557)
Effect of Cash Collateral Netting	(18)	0
Net Carrying Value on Balance Sheet, Liabilities	74	8
Commodity Contracts [Member]
Assets:
Derivative contracts	778	682
Effect of Counterparty Netting	(706)	(557)
Effect of Cash Collateral Netting	0	(12)
Derivative contracts, net assets	72	113
Cash Collateral Received Not Offset	0	0
Liabilities:
Derivative contracts	724	557
Effect of Counterparty Netting	(706)	(557)
Effect of Cash Collateral Netting	(18)	0
Derivative contracts, net liabilities	0	0
Cash Collateral Paid Not Offset	(86)	(31)
Physical Purchase Contracts [Member]
Assets:
Derivative contracts	1
Derivative contracts, net assets	1
Liabilities:
Derivative contracts	11	6
Derivative contracts, net liabilities	11	6
Foreign Currency Contracts [Member]
Assets:
Derivative contracts	1	3
Derivative contracts, net assets	1	3
Fair Value, Inputs, Level 1 [Member]
Assets:
Investments of certain benefit plans	57	64
Total gross fair value, assets	811	716
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	706	522
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	753	649
Liabilities:
Derivative contracts	706	522
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Assets:
Derivative contracts	0
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	1	3
Fair Value, Inputs, Level 2 [Member]
Assets:
Investments of certain benefit plans	0	0
Total gross fair value, assets	26	33
Liabilities:
Environmental credit obligations	63	2
Total gross fair value, liabilities	92	43
Fair Value, Inputs, Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	25	33
Liabilities:
Derivative contracts	18	35
Fair Value, Inputs, Level 2 [Member] | Physical Purchase Contracts [Member]
Assets:
Derivative contracts	1
Liabilities:
Derivative contracts	11	6
Fair Value, Inputs, Level 2 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	0	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]
Assets:
Derivative contracts	0
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 3 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	$ 0	$ 0