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Regulatory Matters (Narrative) (Details) $ in Millions | Dec. 31, 2024 USD ($) MW | Dec. 31, 2023 USD ($)
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Regulatory Assets and Liabilities Disclosure [Line Items] |  |
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | $ 671.3 | $ 716.4
COVID-19 related regulatory asset | 2,477.3 | 2,460.2
Regulatory Liabilities | 1,581.7 | 1,789.3
Annual Revenue Increase from Joint Stipulation and Proposed Settlements | $ 28.2 |
Minimum |  |
Regulatory Assets and Liabilities Disclosure [Line Items] |  |
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 15 years |
Maximum |  |
Regulatory Assets and Liabilities Disclosure [Line Items] |  |
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 75 years |
Overrecovered Gas And Fuel Costs |  |
Regulatory Assets and Liabilities Disclosure [Line Items] |  |
Regulatory Liabilities | $ 21.4 | $ 144.5
NIPSCO |  |
Regulatory Assets and Liabilities Disclosure [Line Items] |  |
Gas Peaker Capacity | MW | 400 |

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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478742/980-340-50-1 + Details
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- Definition Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478742/980-340-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 55 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478098/980-340-55-2 + Details
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