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Pension and Other Postretirement Benefits (Schedule Of Reconciliation Of The Plans Funded Status And Amounts Reflected) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]      
Noncurrent liabilities $ (261.5) $ (303.5)  
COVID-19 related regulatory asset 2,492.2 1,930.5  
Regulatory Liabilities 1,980.0 2,065.5  
Unrecognized Pension Benefit And Other Postretirement Benefit Costs      
Defined Benefit Plan Disclosure [Line Items]      
Regulatory Liabilities 0.0 0.0  
Unrecognized Pension Benefit And Other Postretirement Benefit Costs      
Defined Benefit Plan Disclosure [Line Items]      
COVID-19 related regulatory asset 512.1 583.3  
Fair Value, Inputs, Level 1, 2 and 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year 2,404.1    
Fair value of plan assets at end of year 2,275.4 2,404.1  
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 2,058.4 2,130.5  
Service cost 30.2 32.0 $ 29.2
Interest cost 31.4 51.6 72.3
Plan participants' contributions 0.0 0.0  
Plan amendments 0.0 0.0  
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) (68.7) 140.1  
Defined Benefit Plan, Benefit Obligation, Benefits Paid 198.9 174.5  
Estimated benefits paid by incurred subsidy 0.0 0.0  
Spinoff to Eversource 0.0 (121.3)  
Projected benefit obligation at end of year 1,852.4 2,058.4 2,130.5
Actual return on plan assets 58.9 329.9  
Employer contributions 4.0 2.9  
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant 0.0 0.0  
Benefits paid (198.9) (174.6)  
Spinoff to Eversource 0.0 121.4  
Defined Benefit Plan, Funded (Unfunded) Status of Plan 129.3 59.3  
Noncurrent assets 159.3 91.4  
Current liabilities (2.8) (2.9)  
Noncurrent liabilities (27.2) (29.2)  
Net amount recognized at end of year 129.3 59.3  
Unrecognized prior service cost 0.3 0.3  
Unrecognized actuarial loss 438.0 497.2  
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income Or Regulatory Asset Or Liability 438.3 497.5  
Pension Plan | Underfunded Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 2,026.3    
Projected benefit obligation at end of year 1,822.4 2,026.3  
Fair value of plan assets at beginning of year 2,117.7    
Fair value of plan assets at end of year 1,981.7 2,117.7  
Defined Benefit Plan, Funded (Unfunded) Status of Plan 159.3 91.4  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year 2,117.7 2,080.9  
Fair value of plan assets at end of year 1,981.7 2,117.7 2,080.9
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 590.8 576.5  
Service cost 6.2 6.6 5.1
Interest cost 9.9 15.4 19.2
Plan participants' contributions 4.2 4.1  
Plan amendments 0.1 0.0  
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) (14.8) 24.8  
Defined Benefit Plan, Benefit Obligation, Benefits Paid 40.6 37.0  
Estimated benefits paid by incurred subsidy 0.4 0.4  
Spinoff to Eversource 0.0 0.0  
Projected benefit obligation at end of year 556.2 590.8 576.5
Actual return on plan assets 23.9 36.3  
Employer contributions 19.8 21.6  
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant 4.2 4.1  
Benefits paid (40.6) (37.0)  
Spinoff to Eversource 0.0 0.0  
Defined Benefit Plan, Funded (Unfunded) Status of Plan (262.5) (304.4)  
Noncurrent assets 0.0 0.0  
Current liabilities (1.0) (0.9)  
Net amount recognized at end of year (262.5) (304.4)  
Unrecognized prior service cost (7.8) (10.1)  
Unrecognized actuarial loss 88.5 116.4  
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income Or Regulatory Asset Or Liability 80.7 106.3  
Other Postretirement Benefits | Fair Value, Inputs, Level 1, 2 and 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year 286.4 261.4  
Fair value of plan assets at end of year $ 293.7 $ 286.4 $ 261.4