Fair Value Measurements, Recurring (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Assets:
Investments of certain benefit plans	$ 74	$ 75
Total gross fair value, assets	674	760
Effect of Counterparty Netting	(570)	(557)
Effect of Cash Collateral Netting	0	(12)
Net Carrying Value on Balance Sheet, Assets	104	191
Liabilities:
Environmental credit obligations	30	2
Total gross fair value, liabilities	680	565
Effect of Counterparty Netting	(570)	(557)
Effect of Cash Collateral Netting	(61)	0
Net Carrying Value on Balance Sheet, Liabilities	49	8
Commodity Contracts [Member]
Assets:
Derivative contracts	595	682
Effect of Counterparty Netting	(570)	(557)
Effect of Cash Collateral Netting	0	(12)
Derivative contracts, net assets	25	113
Cash Collateral Received Not Offset	0	0
Liabilities:
Derivative contracts	631	557
Effect of Counterparty Netting	(570)	(557)
Effect of Cash Collateral Netting	(61)	0
Derivative contracts, net liabilities	0	0
Cash Collateral Paid Not Offset	(108)	(31)
Foreign Currency Contracts [Member]
Assets:
Derivative contracts	5	3
Derivative contracts, net assets	5	3
Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	19	6
Derivative contracts, net liabilities	19	6
Fair Value, Inputs, Level 1 [Member]
Assets:
Investments of certain benefit plans	63	64
Total gross fair value, assets	633	716
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	606	522
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	565	649
Liabilities:
Derivative contracts	606	522
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	5	3
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	30	33
Liabilities:
Environmental credit obligations	30	2
Total gross fair value, liabilities	74	43
Fair Value, Inputs, Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	30	33
Liabilities:
Derivative contracts	25	35
Fair Value, Inputs, Level 2 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	0	0
Fair Value, Inputs, Level 2 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	19	6
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] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	0	0
Fair Value, Inputs, Level 3 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	$ 0	$ 0