v2.4.0.8
Business Segment Information (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Segment Reporting Information [Line Items]        
Revenues $ 1,212.3 $ 1,038.8 $ 3,006.6 $ 2,687.0
Consolidated Operating Income (Loss) 193.5 205.0 621.6 602.0
Gas Distribution Operations [Member]
       
Segment Reporting Information [Line Items]        
Revenues 572.4 443.9 1,717.5 1,504.2
Consolidated Operating Income (Loss) 50.0 43.4 284.1 253.0
Gas Distribution Operations [Member] | Unaffiliated [Member]
       
Segment Reporting Information [Line Items]        
Revenues 572.4 443.8 1,717.3 1,503.9
Gas Distribution Operations [Member] | Intersegment [Member]
       
Segment Reporting Information [Line Items]        
Revenues 0 0.1 0.2 0.3
Columbia Pipeline Group Operations [Member]
       
Segment Reporting Information [Line Items]        
Revenues 273.8 241.0 575.2 516.4
Consolidated Operating Income (Loss) 88.8 91.5 222.3 230.1
Columbia Pipeline Group Operations [Member] | Unaffiliated [Member]
       
Segment Reporting Information [Line Items]        
Revenues 242.3 209.5 500.7 442.5
Columbia Pipeline Group Operations [Member] | Intersegment [Member]
       
Segment Reporting Information [Line Items]        
Revenues 31.5 31.5 74.5 73.9
Electric Operations [Member]
       
Segment Reporting Information [Line Items]        
Revenues 385.1 377.4 762.7 730.5
Consolidated Operating Income (Loss) 59.5 70.3 124.7 116.5
Electric Operations [Member] | Unaffiliated [Member]
       
Segment Reporting Information [Line Items]        
Revenues 384.9 377.2 762.3 730.1
Electric Operations [Member] | Intersegment [Member]
       
Segment Reporting Information [Line Items]        
Revenues 0.2 0.2 0.4 0.4
Corporate/Other [Member]
       
Segment Reporting Information [Line Items]        
Revenues 122.7 123.6 258.0 236.5
Consolidated Operating Income (Loss) (4.8) (0.2) (9.5) 2.4
Corporate/Other [Member] | Unaffiliated [Member]
       
Segment Reporting Information [Line Items]        
Revenues 12.7 8.3 26.3 10.5
Corporate/Other [Member] | Intersegment [Member]
       
Segment Reporting Information [Line Items]        
Revenues 110.0 115.3 231.7 226.0
Eliminations [Member]
       
Segment Reporting Information [Line Items]        
Revenues $ (141.7) $ (147.1) $ (306.8) $ (300.6)