Other Commitments And Contingencies (Narrative) (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 05, 2014
USD ($)
Other Commitments And Contingencies [Line Items]      
Guarantees $ 2,768.1    
Line of Credit Facility, Maximum Borrowing Capacity $ 2,600.0    
Ozone Level Maximum 70 ppb    
Percentage Reduction in Methane Emissions 95.00%    
Hours of Operation 26,000    
Replacement Years 3 years    
Columbia Pipeline Group      
Other Commitments And Contingencies [Line Items]      
Commercial Paper $ 0.0    
Line of Credit Facility Used For Credit Support for Subsidiaries 750.0    
Line of Credit Facility Used For Corporate Purposes 750.0    
Revolving Credit Facility      
Other Commitments And Contingencies [Line Items]      
Credit facilities borrowings 15.0 $ 15.0  
Revolving Credit Facility | Columbia Pipeline Group      
Other Commitments And Contingencies [Line Items]      
Credit facilities borrowings 0.0    
Letters of Credit      
Other Commitments And Contingencies [Line Items]      
Letters of Credit Outstanding, Amount 0.0 $ 0.0  
Letters of Credit | Columbia Pipeline Group      
Other Commitments And Contingencies [Line Items]      
Letters of Credit Outstanding, Amount 18.1    
Commercial Paper | Columbia Pipeline Group      
Other Commitments And Contingencies [Line Items]      
Line of Credit Facility, Maximum Borrowing Capacity 1,000.0    
Revolving Credit Facility      
Other Commitments And Contingencies [Line Items]      
Line of Credit Facility, Maximum Borrowing Capacity 500.0   $ 1,500.0
Revolving Credit Facility | Columbia Pipeline Group      
Other Commitments And Contingencies [Line Items]      
Line of Credit Facility, Maximum Borrowing Capacity 1,500.0    
Letters of Credit      
Other Commitments And Contingencies [Line Items]      
Line of Credit Facility, Maximum Borrowing Capacity 50.0    
Letters of Credit | Columbia Pipeline Group      
Other Commitments And Contingencies [Line Items]      
Line of Credit Facility, Maximum Borrowing Capacity 250.0    
Guarantee of Indebtedness of Others      
Other Commitments And Contingencies [Line Items]      
Guarantees 2,750.0    
Letters of Credit      
Other Commitments And Contingencies [Line Items]      
Guarantees $ 18.1