v2.4.0.8
Other Commitments And Contingencies (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 6 Months Ended 12 Months Ended 0 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Jun. 30, 2013
MGP Sites
Dec. 31, 2012
MGP Sites
Jun. 30, 2013
Millennium Pipeline Company, L.L.C [Member]
Jun. 30, 2013
Columbia Transmission [Member]
Dec. 31, 2012
Columbia Transmission [Member]
Jun. 30, 2013
Guarantees Of Subsidiaries Debt [Member]
Jun. 30, 2013
Guarantees Supporting Energy Commodity Transactions Of Subsidiaries [Member]
Jun. 30, 2013
Letters Of Credit [Member]
Jun. 30, 2013
Other Guarantees [Member]
Jun. 30, 2013
Commercial Paper [Member]
Jun. 30, 2013
Accounts Receivable Securitization [Member]
Dec. 31, 2013
Maximum [Member]
Northern Indiana [Member]
Dec. 31, 2013
Minimum [Member]
Northern Indiana [Member]
Jun. 30, 2013
Letters Of Credit [Member]
Dec. 31, 2012
Letters Of Credit [Member]
May 31, 2012
TerminationDateMay152017 [Member]
May 15, 2012
Revolving Credit Facility [Member]
Jun. 30, 2013
Revolving Credit Facility [Member]
May 31, 2012
Revolving Credit Facility [Member]
Other Commitments And Contingencies [Line Items]                                          
Guarantees $ 7,720.2       $ 16.2     $ 7,135.5 $ 37.0 $ 38.6 $ 131.4 $ 117.6 $ 260.1                
Revolving credit facility, maximum                                   1,500.0     1,500.0
Revolving Credit Facility Expiration Date                                     May 15, 2017    
Line of Credit Facility, Amount Outstanding 0 44.0                           38.6 36.4     0  
Commercial paper 117.6 499.6                                      
Accounts receivable securitization facility borrowings 260.1 233.3                                      
Additional purchase and sales agreement guarantees 42.0                                        
Percentage of interest in Millennium 47.50%       47.50%                                
Fair value of guarantee obligations         1.5                                
Gain (Loss) Related to Litigation Settlement 17.5                                        
Recorded reserves to cover environmental remediation at various sites 156.4 160.6                                      
Payments for capital improvements                           865 835            
Remaining Payments for Capital Improvements                           415 385            
Number of waste disposal sites identified by program     67                                    
Original number of facilities AOC covered under conduct characterization and remediation activities, approximately           245                              
Number of liquid removal points AOC covered under conduct characterization and remediation activities           13,000                              
Number of mercury measurement stations AOC covered under conduct characterization and remediation activities           2,200                              
Number of storage well locations AOC covered under conduct characterization and remediation activities           3,700                              
Proposed penalty of NOV asserts violations of Pennsylvania Clean Streams law and Pennsylvania Solid Waste Management act           1                              
Increased liability for estimated remediation costs             25.6                            
Liability for estimated remediation costs     134.6 132.6   15.5 21.7                            
Reasonably possible remediation costs variance from reserve     $ 25                                    
Remaining number of facilities AOC covered under conduct characterization and remediation activities, approximately           50