Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets		$ 113	$ 113
Total Non Current Regulatory Assets		$ 587	530
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		6 years
Total regulatory assets		$ 700	643
Total Current Regulatory Liabilities		$ 48	81
Remaining Recovery Period of Regulatory Liabilities		1 year
Total Non Current Regulatory Liabilities		$ 1,058	1,090
Total regulatory liabilities		1,106	1,171
Overcollection of Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities		47	80
Deferred Income Tax Charge [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Liabilities		174	209
Asset Retirement Obligation Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Liabilities		863	863
Other Regulatory Liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities		1	1
Total Non Current Regulatory Liabilities		21	18
El Salvador Tariff Recoveries
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets		40	56
Pension Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Assets	[1]	244	262
Deferred Midwest Independent Service Operator Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Assets		61	75
Environmental Restoration Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Assets		81	85
Other Regulatory Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets		73	57
Total Non Current Regulatory Assets		126	108
Petersburg Unit Retirement Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Assets		$ 75	$ 0

[1] Past expenditures on which the Company earns a rate of return.