Fair Value Measurements, Recurring (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets
Total gross fair value, assets	$ 489	$ 498
Effect of counterparty netting	(386)	(373)
Effect of cash collateral netting	0	(18)
Net carrying value on Balance Sheet, assets	103	107
Liabilities
Environmental credit obligations	62	96
Total gross fair value, liabilities	506	505
Effect of counterparty netting	(386)	(373)
Effect of cash collateral netting	(58)	(32)
Net carrying value on Balance Sheet, liabilities	62	100
Assets Held in Trust [Member]
Assets
Investments of certain benefit plans	83	82
Commodity Contracts [Member]
Assets
Derivative contracts	386	403
Effect of counterparty netting	(386)	(373)
Effect of cash collateral netting	0	(18)
Derivative contracts, net assets	0	12
Cash collateral received not offset	0	0
Liabilities
Derivative contracts	444	405
Effect of counterparty netting	(386)	(373)
Effect of cash collateral netting	(58)	(32)
Derivative contracts, net liabilities	0	0
Cash collateral paid not offset	(120)	(44)
Physical Purchase Contracts [Member]
Assets
Derivative contracts	10	13
Derivative contracts, net assets	10	13
Foreign Currency Contracts [Member]
Assets
Derivative contracts	10
Derivative contracts, net assets	10
Liabilities
Derivative contracts		4
Derivative contracts, net liabilities		4
Fair Value, Inputs, Level 1 [Member]
Assets
Total gross fair value, assets	471	477
Liabilities
Environmental credit obligations	0	0
Total gross fair value, liabilities	444	409
Fair Value, Inputs, Level 1 [Member] | Assets Held in Trust [Member]
Assets
Investments of certain benefit plans	75	74
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets
Derivative contracts	386	403
Liabilities
Derivative contracts	444	405
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Assets
Derivative contracts	0	0
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets
Derivative contracts	10
Liabilities
Derivative contracts		4
Fair Value, Inputs, Level 2 [Member]
Assets
Total gross fair value, assets	10	13
Liabilities
Environmental credit obligations	62	96
Total gross fair value, liabilities	62	96
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	10	13
Fair Value, Inputs, Level 2 [Member] | Foreign Currency Contracts [Member]
Assets
Derivative contracts	0
Liabilities
Derivative contracts		0
Fair Value, Inputs, Level 3 [Member]
Assets
Total gross fair value, assets	8	8
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	8	8
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	0
Fair Value, Inputs, Level 3 [Member] | Foreign Currency Contracts [Member]
Assets
Derivative contracts	$ 0
Liabilities
Derivative contracts		$ 0