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Other Commitments And Contingencies (Narrative) (Details) $ in Millions |  | 9 Months Ended |
--- | --- | --- | ---
Apr. 17, 2015 USD ($) | Sep. 30, 2016 USD ($) | Dec. 31, 2015 USD ($)
Other Commitments And Contingencies [Line Items] |  |  |
Proposed Pipeline Safety Rule, time period for investigation and repair/replace activity on facilities |  | 15 years |
Recorded reserves to cover environmental remediation at various sites |  | $ 116.9 | $ 123.2
Number of countries agreeing to limit GHGs |  | 194 |
Proposed reduction in GHG levels |  | 26-28% |
Estimated Cost of Compliance with Effluent Limitations Guidelines |  | $ 170.0 |
Estimated Cost of Compliance with Coal Combustion Residuals | $ 230.0 |  |
Transmission Upgrade Agreement Multiplier |  | 1.71 |
MGP Sites |  |  |
Other Commitments And Contingencies [Line Items] |  |  |
Number of waste disposal sites identified by program |  | 64 |
Liability for Estimated Remediation Costs |  | $ 108.3 | $ 110.4
Reasonably possible remediation costs variance from reserve |  | 25.0 |
NIPSCO |  |  |
Other Commitments And Contingencies [Line Items] |  |  |
Upgrade Sponsors Liability related to Portion Collected for Taxes on TUA |  | 8.6 |
Gain (Loss) on Contract Termination |  | 16.0 |
Letters Of Credit |  |  |
Other Commitments And Contingencies [Line Items] |  |  |
Guarantor Obligations, Maximum Exposure, Undiscounted |  | $ 14.7 |
Maximum |  |  |
Other Commitments And Contingencies [Line Items] |  |  |
Ozone Level |  | 75 ppb |
Estimated Cost of Compliance with Clean Water Act, minimum |  | $ 35.0 |
Maximum | NIPSCO |  |  |
Other Commitments And Contingencies [Line Items] |  |  |
Severance Costs |  | 15.0 |
Total Severance and Contract Termination Cost |  | $ 31.0 |
Minimum |  |  |
Other Commitments And Contingencies [Line Items] |  |  |
Ozone Level |  | 70 ppb |
Estimated Cost of Compliance with Clean Water Act, minimum |  | $ 0.0 |
Minimum | NIPSCO |  |  |
Other Commitments And Contingencies [Line Items] |  |  |
Cost to Maintain and Operate Current Fleet of Coal-Fired Generating Units |  | 1,000.0 |
Severance Costs |  | 10.0 |
Total Severance and Contract Termination Cost |  | $ 26.0 |

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