Fair Value Measurements, Recurring (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets
Total gross fair value, assets	$ 718	$ 2,865
Effect of counterparty netting	(612)	(2,669)
Effect of cash collateral netting	0	(34)
Net carrying value on Balance Sheet, assets	106	162
Liabilities
Environmental credit obligations	2	13
Total gross fair value, liabilities	683	2,700
Effect of counterparty netting	(612)	(2,669)
Effect of cash collateral netting	(56)	(12)
Net carrying value on Balance Sheet, liabilities	15	19
Assets Held in Trust [Member]
Assets
Investments of certain benefit plans	74	69
Commodity Contracts [Member]
Assets
Derivative contracts	617	2,792
Effect of counterparty netting	(612)	(2,669)
Effect of cash collateral netting	0	(34)
Derivative contracts, net assets	5	89
Cash collateral received not offset	0	0
Liabilities
Derivative contracts	668	2,681
Effect of counterparty netting	(612)	(2,669)
Effect of cash collateral netting	(56)	(12)
Derivative contracts, net liabilities	0	0
Cash collateral paid not offset	(84)	(136)
Physical Purchase Contracts [Member]
Liabilities
Derivative contracts	3	5
Derivative contracts, net liabilities	3	5
Foreign Currency Contracts [Member]
Assets
Derivative contracts	27	4
Derivative contracts, net assets	27	4
Liabilities
Derivative contracts	10	1
Derivative contracts, net liabilities	10	1
Fair Value, Inputs, Level 1 [Member]
Assets
Total gross fair value, assets	709	2,856
Liabilities
Environmental credit obligations	0	0
Total gross fair value, liabilities	678	2,682
Fair Value, Inputs, Level 1 [Member] | Assets Held in Trust [Member]
Assets
Investments of certain benefit plans	65	60
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets
Derivative contracts	617	2,792
Liabilities
Derivative contracts	668	2,681
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Liabilities
Derivative contracts	0	0
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets
Derivative contracts	27	4
Liabilities
Derivative contracts	10	1
Fair Value, Inputs, Level 2 [Member]
Assets
Total gross fair value, assets	0	0
Liabilities
Environmental credit obligations	2	13
Total gross fair value, liabilities	5	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]
Liabilities
Derivative contracts	3	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]
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