Fair Value Measurements, Recurring (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets:
Total gross fair value, assets	$ 711	$ 2,865
Effect of counterparty netting	(560)	(2,669)
Effect of cash collateral netting	(30)	(34)
Net carrying value on Balance Sheet, assets	121	162
Liabilities:
Environmental credit obligations	17	13
Total gross fair value, liabilities	616	2,700
Effect of counterparty netting	(560)	(2,669)
Effect of cash collateral netting	(13)	(12)
Net carrying value on Balance Sheet, liabilities	43	19
Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	70	69
Commodity Contracts [Member]
Assets:
Derivative contracts	638	2,792
Effect of counterparty netting	(560)	(2,669)
Effect of cash collateral netting	(30)	(34)
Derivative contracts, net assets	48	89
Cash collateral received not offset	0	0
Liabilities:
Derivative contracts	573	2,681
Effect of counterparty netting	(560)	(2,669)
Effect of cash collateral netting	(13)	(12)
Derivative contracts, net liabilities	0	0
Cash collateral paid not offset	(47)	(136)
Foreign Currency Contracts [Member]
Assets:
Derivative contracts	3	4
Derivative contracts, net assets	3	4
Liabilities:
Derivative contracts	20	1
Derivative contracts, net liabilities	20	1
Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	6	5
Derivative contracts, net liabilities	6	5
Fair Value, Inputs, Level 1 [Member]
Assets:
Total gross fair value, assets	702	2,856
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	593	2,682
Fair Value, Inputs, Level 1 [Member] | Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	61	60
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	638	2,792
Liabilities:
Derivative contracts	573	2,681
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	3	4
Liabilities:
Derivative contracts	20	1
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Total gross fair value, assets	0	0
Liabilities:
Environmental credit obligations	17	13
Total gross fair value, liabilities	23	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] | Foreign Currency Contracts [Member]
Assets:
Derivative contracts	0	0
Liabilities:
Derivative contracts	0	0
Fair Value, Inputs, Level 2 [Member] | Physical Purchase Contracts [Member]
Liabilities:
Derivative contracts	6	5
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] | Foreign Currency 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