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Summary of Significant Accounting Policies and Other Matters - Investments (Details) - Stagecoach Gas Services LLC - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 9 Months Ended
Jul. 31, 2021
May 31, 2021
Mar. 31, 2022
Sep. 30, 2021
Jun. 30, 2021
Mar. 31, 2021
Schedule of Equity Method Investments [Line Items]            
Loss on sale of investment (pre-tax)       $ 211.0    
Loss on sale of investment       147.0    
Equity method investments         $ 630.0 $ 667.0
Con Edison Transmission | Subsidiaries            
Schedule of Equity Method Investments [Line Items]            
Proceeds from sale $ 1,195.0 $ 1,225.0        
Ownership percentage   50.00%        
Impairment charge       $ 414.0    
Con Edison Transmission | Scenario, Forecast | Subsidiaries            
Schedule of Equity Method Investments [Line Items]            
Proceeds from sale     $ 30.0      
CET Gas | Subsidiaries            
Schedule of Equity Method Investments [Line Items]            
Proceeds from sale $ 614.0 $ 612.5        
CET Gas | Scenario, Forecast | Subsidiaries            
Schedule of Equity Method Investments [Line Items]            
Proceeds from sale     $ 15.0