Fair Value Measurements, Recurring (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets:
Total gross fair value, assets	$ 974	$ 2,865
Effect of counterparty netting	(803)	(2,669)
Effect of cash collateral netting	(7)	(34)
Net carrying value on Balance Sheet, assets	164	162
Liabilities:
Environmental credit obligations	6	13
Total gross fair value, liabilities	837	2,700
Effect of counterparty netting	(803)	(2,669)
Effect of cash collateral netting	(12)	(12)
Net carrying value on Balance Sheet, liabilities	22	19
Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	69	69
Commodity Contracts [Member]
Assets:
Derivative contracts	863	2,792
Effect of counterparty netting	(803)	(2,669)
Effect of cash collateral netting	(7)	(34)
Derivative contracts, net assets	53	89
Cash collateral received not offset	0	0
Liabilities:
Derivative contracts	815	2,681
Effect of counterparty netting	(803)	(2,669)
Effect of cash collateral netting	(12)	(12)
Derivative contracts, net liabilities	0	0
Cash collateral paid not offset	(80)	(136)
Physical Purchase Contracts [Member]
Assets:
Derivative contracts	9
Derivative contracts, net assets	9
Liabilities:
Derivative contracts	5	5
Derivative contracts, net liabilities	5	5
Foreign Currency Contracts [Member]
Assets:
Derivative contracts	33	4
Derivative contracts, net assets	33	4
Liabilities:
Derivative contracts	11	1
Derivative contracts, net liabilities	11	1
Fair Value, Inputs, Level 1 [Member]
Assets:
Total gross fair value, assets	956	2,856
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	826	2,682
Fair Value, Inputs, Level 1 [Member] | Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	60	60
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	863	2,792
Liabilities:
Derivative contracts	815	2,681
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	33	4
Liabilities:
Derivative contracts	11	1
Fair Value, Inputs, Level 2 [Member]
Assets:
Total gross fair value, assets	9	0
Liabilities:
Environmental credit obligations	6	13
Total gross fair value, liabilities	11	18
Fair Value, Inputs, Level 2 [Member] | Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	0	0
Fair Value, Inputs, Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	0	0
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 2 [Member] | Physical Purchase Contracts [Member]
Assets:
Derivative contracts	9
Liabilities:
Derivative contracts	5	5
Fair Value, Inputs, Level 2 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	0	0
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 3 [Member]
Assets:
Total gross fair value, assets	9	9
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	0	0
Fair Value, Inputs, Level 3 [Member] | Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	9	9
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
Liabilities:
Derivative contracts	$ 0	$ 0