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Pension, OPEB and Savings Plans (Assumptions Used To Determine The Benefit Obligations And Net Periodic Benefit Costs) (Details)
6 Months Ended 12 Months Ended
Jun. 30, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Jul. 01, 2019
Dec. 31, 2017
Pension Benefits [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Discount Rate 4.41% 2.61% 3.30%   3.65% 4.41%
Expected Return on Plan Assets 7.80% 7.70% 7.80% 7.80%    
Rate of Compensation Increase   4.40% 3.90%     3.90%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate   6.00% 6.00% 6.00%    
Service Cost Interest Rate   3.49% 4.58% 3.88%    
Interest Cost Interest Rate   2.87% 4.03% 3.35%    
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase   3.90% 3.90% 3.90%    
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted-Average Interest Crediting Rate   6.00% 6.00% 6.00%    
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate   3.30% 4.41% 3.73%    
Other Benefits [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Discount Rate   2.46% 3.20%     4.31%
Expected Return on Plan Assets   7.70% 7.79% 7.80%    
Rate of Compensation Increase   4.40% 3.90%     3.90%
Service Cost Interest Rate   3.50% 4.48% 3.90%    
Interest Cost Interest Rate   2.87% 3.91% 3.39%    
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase   3.90% 3.90% 3.90%    
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate   3.20% 4.31% 3.76%    
Immediate Rate   6.37% 6.68%     7.28%
Ultimate Rate   4.75% 4.75%     4.75%
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Benefits [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Discount Rate   2.98% 3.52% 4.60%    
Expected Return on Plan Assets   7.60%        
Rate of Compensation Increase   3.95% 3.25% 3.25%    
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate   3.75% 3.75% 3.75%    
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Other Benefits [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Discount Rate   3.08% 3.60% 4.67%    
Rate of Compensation Increase   3.95% 3.25% 3.25%    
Immediate Rate   6.70% 6.94% 8.03%    
Ultimate Rate   4.75% 4.75% 4.75%