Equity Method Investments (Schedule Of Immaterial Nature Of Equity Investments) (Details) - USD ($)
$ in Millions
 1 Months Ended 12 Months Ended
Feb. 11, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]        
Contribution of capital from parent $ 1,217.3      
Partners' Capital Account, Distributions       $ 113.0
Millennium Pipeline        
Schedule of Equity Method Investments [Line Items]        
Net Revenues   $ 206.3    
Operating Income   136.1    
Net Income   98.0    
Current Assets   35.7    
Noncurrent Assets   987.1    
Current Liabilities   44.4    
Noncurrent Liabilities   535.8    
Total Members’ Equity   442.6    
Contribution of capital from parent [1]   1.4    
Partners' Capital Account, Distributions [1]   47.5    
Millennium Pipeline | Predecessor        
Schedule of Equity Method Investments [Line Items]        
Net Revenues     $ 190.5 157.8
Operating Income     128.8 101.3
Net Income     89.6 63.0
Current Assets     32.1 38.3
Noncurrent Assets     1,016.3 1,033.8
Current Liabilities     42.6 58.8
Noncurrent Liabilities     568.3 599.7
Total Members’ Equity     437.5 413.6
Contribution of capital from parent [1]     2.6 16.6
Partners' Capital Account, Distributions [1]     35.6 29.0
Hardy Storage        
Schedule of Equity Method Investments [Line Items]        
Net Revenues   23.4    
Operating Income   15.3    
Net Income   10.3    
Current Assets   12.1    
Noncurrent Assets   155.5    
Current Liabilities   19.3    
Noncurrent Liabilities   68.5    
Total Members’ Equity   79.8    
Contribution of capital from parent [1]   0.0    
Partners' Capital Account, Distributions [1]   2.6    
Hardy Storage | Predecessor        
Schedule of Equity Method Investments [Line Items]        
Net Revenues     23.6 24.4
Operating Income     16.1 16.5
Net Income     10.6 10.6
Current Assets     12.0 12.5
Noncurrent Assets     157.4 160.2
Current Liabilities     17.1 18.3
Noncurrent Liabilities     77.4 85.7
Total Members’ Equity     74.9 68.7
Contribution of capital from parent [1]     0.0 0.0
Partners' Capital Account, Distributions [1]     2.2 3.1
Pennant        
Schedule of Equity Method Investments [Line Items]        
Net Revenues   34.6    
Operating Income   17.8    
Net Income   17.8    
Current Assets   11.0    
Noncurrent Assets   389.6    
Noncurrent Liabilities   8.4    
Total Members’ Equity   392.2    
Contribution of capital from parent [1]   0.0    
Partners' Capital Account, Distributions [1]   7.1    
Partners' Capital Account, Return of Capital [1]   $ 16.0    
Pennant | Predecessor        
Schedule of Equity Method Investments [Line Items]        
Net Revenues     8.5 2.0
Operating Income     (2.4) 1.3
Net Income     (2.4) 1.3
Current Assets     23.7 34.1
Noncurrent Assets     380.0 231.9
Noncurrent Liabilities     8.6 11.4
Total Members’ Equity     395.1 254.6
Contribution of capital from parent [1]     66.6 108.9
Partners' Capital Account, Distributions [1]     0.0 0.0
Partners' Capital Account, Return of Capital [1]     $ 0.0 $ 0.0
[1] Contribution and distribution data represents the Partnership's portion based on the Partnership's ownership percentage of each investment.