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Other Commitments And Contingencies (Narrative) (Details)
 6 Months Ended 31 Months Ended
Jun. 30, 2021
USD ($)
Rate
Mar. 31, 2021
USD ($)
Jul. 01, 2021
USD ($)
Dec. 31, 2020
USD ($)
Jul. 26, 2019
USD ($)
Other Commitments And Contingencies [Line Items]          
Guaranty Liabilities $ 519,500,000   $ 544,700,000    
Litigation Settlement, Amount Awarded to Other Party         $ 143,000,000
Recorded reserves to cover environmental remediation at various sites $ 93,300,000     $ 92,600,000  
Wind Power Purchase Agreement, Purchase Percentage | Rate 100.00%        
Restructuring and Related Cost, Expected Cost $ 41,000,000        
MGP Sites          
Other Commitments And Contingencies [Line Items]          
Number of waste disposal sites identified by program 54        
Liability for Estimated Remediation Costs $ 87,100,000     85,000,000.0  
Reasonably possible remediation costs variance from reserve $ 17,000,000        
Columbia Of Massachusetts          
Other Commitments And Contingencies [Line Items]          
Gas Meters Affected 7,500        
Businesses Impacted by Incident 700        
Plea Agreement Criminal Fine $ 53,030,116        
Pipeline Replacement Expenses   $ 258,000,000      
Standby Letters of Credit          
Other Commitments And Contingencies [Line Items]          
Long-term Line of Credit $ 14,100,000     $ 15,200,000