Fair Value Measurements, Recurring (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets
Total gross fair value, assets	$ 885	$ 498
Effect of counterparty netting	(677)	(373)
Effect of cash collateral netting	(48)	(18)
Net carrying value on Balance Sheet, assets	160	107
Liabilities
Environmental credit obligations	94	96
Total gross fair value, liabilities	840	505
Effect of counterparty netting	(677)	(373)
Effect of cash collateral netting	(59)	(32)
Net carrying value on Balance Sheet, liabilities	104	100
Assets Held in Trust [Member]
Assets
Investments of certain benefit plans	90	82
Commodity Contracts [Member]
Assets
Derivative contracts	785	403
Effect of counterparty netting	(677)	(373)
Effect of cash collateral netting	(48)	(18)
Derivative contracts, net assets	60	12
Cash collateral received not offset	0	0
Liabilities
Derivative contracts	736	405
Effect of counterparty netting	(677)	(373)
Effect of cash collateral netting	(59)	(32)
Derivative contracts, net liabilities	0	0
Cash collateral paid not offset	(55)	(44)
Physical Purchase Contracts [Member]
Assets
Derivative contracts	6	13
Derivative contracts, net assets	6	13
Liabilities
Derivative contracts	5
Derivative contracts, net liabilities	5
Foreign Currency Contracts [Member]
Assets
Derivative contracts	4
Derivative contracts, net assets	4
Liabilities
Derivative contracts	5	4
Derivative contracts, net liabilities	5	4
Fair Value, Inputs, Level 1 [Member]
Assets
Total gross fair value, assets	873	477
Liabilities
Environmental credit obligations	0	0
Total gross fair value, liabilities	741	409
Fair Value, Inputs, Level 1 [Member] | Assets Held in Trust [Member]
Assets
Investments of certain benefit plans	84	74
Fair Value, Inputs, Level 1 [Member] | Commodity Contracts [Member]
Assets
Derivative contracts	785	403
Liabilities
Derivative contracts	736	405
Fair Value, Inputs, Level 1 [Member] | Physical Purchase Contracts [Member]
Assets
Derivative contracts	0	0
Liabilities
Derivative contracts	0
Fair Value, Inputs, Level 1 [Member] | Foreign Currency Contracts [Member]
Assets
Derivative contracts	4
Liabilities
Derivative contracts	5	4
Fair Value, Inputs, Level 2 [Member]
Assets
Total gross fair value, assets	6	13
Liabilities
Environmental credit obligations	94	96
Total gross fair value, liabilities	99	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	6	13
Liabilities
Derivative contracts	5
Fair Value, Inputs, Level 2 [Member] | Foreign Currency Contracts [Member]
Assets
Derivative contracts	0
Liabilities
Derivative contracts	0	0
Fair Value, Inputs, Level 3 [Member]
Assets
Total gross fair value, assets	6	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	6	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
Liabilities
Derivative contracts	0
Fair Value, Inputs, Level 3 [Member] | Foreign Currency Contracts [Member]
Assets
Derivative contracts	0
Liabilities
Derivative contracts	$ 0	$ 0