Fair Value Measurements, Recurring (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Assets:
Total gross fair value, assets	$ 709	$ 2,865
Effect of counterparty netting	(620)	(2,669)
Effect of cash collateral netting	(9)	(34)
Net carrying value on Balance Sheet, assets	80	162
Liabilities:
Environmental credit obligations	3	13
Total gross fair value, liabilities	742	2,700
Effect of counterparty netting	(620)	(2,669)
Effect of cash collateral netting	(109)	(12)
Net carrying value on Balance Sheet, liabilities	13	19
Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	71	69
Commodity Contracts [Member]
Assets:
Derivative contracts	634	2,792
Effect of counterparty netting	(620)	(2,669)
Effect of cash collateral netting	(9)	(34)
Derivative contracts, net assets	5	89
Cash collateral received not offset	0	0
Liabilities:
Derivative contracts	729	2,681
Effect of counterparty netting	(620)	(2,669)
Effect of cash collateral netting	(109)	(12)
Derivative contracts, net liabilities	0	0
Cash collateral paid not offset	(50)	(136)
Physical Purchase Contracts [Member]
Assets:
Derivative contracts	2
Derivative contracts, net assets	2
Liabilities:
Derivative contracts	4	5
Derivative contracts, net liabilities	4	5
Foreign Currency Contracts [Member]
Assets:
Derivative contracts	2	4
Derivative contracts, net assets	2	4
Liabilities:
Derivative contracts	6	1
Derivative contracts, net liabilities	6	1
Fair Value, Inputs, Level 1 [Member]
Assets:
Total gross fair value, assets	698	2,856
Liabilities:
Environmental credit obligations	0	0
Total gross fair value, liabilities	735	2,682
Fair Value, Inputs, Level 1 [Member] | Assets Held in Trust [Member]
Assets:
Investments of certain benefit plans	62	60
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivative contracts	634	2,792
Liabilities:
Derivative contracts	729	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	2	4
Liabilities:
Derivative contracts	6	1
Fair Value, Inputs, Level 2 [Member]
Assets:
Total gross fair value, assets	2	0
Liabilities:
Environmental credit obligations	3	13
Total gross fair value, liabilities	7	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	2
Liabilities:
Derivative contracts	4	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