v2.4.0.8
Risk Management Activities Risk Management Activities (Offsetting Assets and Liabilities) (Details) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Offsetting Assets and Liabilities [Line Items]    
Gross Amounts of Recognized Assets $ 73.5 $ 148.2
Gross Amounts Offset in the Statement of Financial Position 0 0
Net Amounts of Assets Presented in the Statement of Financial Position 73.5 148.2
Gross Amounts Not Offset in the Statement of Financial Position (37.4) (72.7)
Net Derivative Position - Assets 36.1 75.5
Gross Amounts of Recognized Liabilities (52.5) (115.5)
Gross Amounts Offset in the Statement of Financial Position-Liabilities 0 0
Net Amounts of Liabilities Presented in the Statement of Financial Position (52.5) (115.5)
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities 37.4 72.7
Net Derivative Position-Liabilities (15.1) (42.8)
Counterparty A [Member]
    
Offsetting Assets and Liabilities [Line Items]    
Gross Amounts of Recognized Assets 27.9 71.8
Gross Amounts Offset in the Statement of Financial Position 0 0
Net Amounts of Assets Presented in the Statement of Financial Position 27.9 71.8
Gross Amounts Not Offset in the Statement of Financial Position (27.9) (71.8)
Net Derivative Position - Assets 0 0
Gross Amounts of Recognized Liabilities (41.9) (103.4)
Gross Amounts Offset in the Statement of Financial Position-Liabilities 0 0
Net Amounts of Liabilities Presented in the Statement of Financial Position (41.9) (103.4)
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities 27.9 71.8
Net Derivative Position-Liabilities (14.0) (31.6)
Counterparty B [Member]
    
Offsetting Assets and Liabilities [Line Items]    
Gross Amounts of Recognized Assets 0.2 0.9
Gross Amounts Offset in the Statement of Financial Position 0 0
Net Amounts of Assets Presented in the Statement of Financial Position 0.2 0.9
Gross Amounts Not Offset in the Statement of Financial Position (9.5) (0.9)
Net Derivative Position - Assets (9.3) 0
Gross Amounts of Recognized Liabilities (9.5) (10.8)
Gross Amounts Offset in the Statement of Financial Position-Liabilities 0 0
Net Amounts of Liabilities Presented in the Statement of Financial Position (9.5) (10.8)
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities 9.5 0.9
Net Derivative Position-Liabilities 0 (9.9)
Counterparty Other [Member]
    
Offsetting Assets and Liabilities [Line Items]    
Gross Amounts of Recognized Assets 45.4 [1] 75.5 [1]
Gross Amounts Offset in the Statement of Financial Position 0 [1] 0 [1]
Net Amounts of Assets Presented in the Statement of Financial Position 45.4 [1] 75.5 [1]
Gross Amounts Not Offset in the Statement of Financial Position 0 [1] 0 [1]
Net Derivative Position - Assets 45.4 [1] 75.5 [1]
Gross Amounts of Recognized Liabilities (1.1) [1] (1.3) [1]
Gross Amounts Offset in the Statement of Financial Position-Liabilities 0 [1] 0 [1]
Net Amounts of Liabilities Presented in the Statement of Financial Position (1.1) [1] (1.3) [1]
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities 0 [1] 0 [1]
Net Derivative Position-Liabilities $ (1.1) [1] $ (1.3) [1]
[1] Amounts in 'Other' include physical positions with counterparties that are part of NiSource's natural gas marketing business as well as fixed-to-variable interest rate swap agreements entered into by NiSource.