Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets and Liabilities Disclosure [Line Items]
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	$ 716.4	$ 1,324.7
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	69 years
COVID-19 related regulatory asset	$ 2,460.2	2,580.8
Regulatory Liabilities	1,789.3	2,012.6
Overrecovered Gas And Fuel Costs
Regulatory Assets and Liabilities Disclosure [Line Items]
Regulatory Liabilities	144.5	$ 20.6
NIPSCO - Electric \| Overrecovered Gas And Fuel Costs
Regulatory Assets and Liabilities Disclosure [Line Items]
Regulatory Liabilities	$ 8.0

Regulatory Assets and Liabilities Disclosure

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 405
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481854/980-405-25-1

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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//1943274/2147481878/980-340-50-1

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-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 55
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481849/980-340-55-2

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Remaining recovery period of regulatory assets for which no return on investment during recovery period is provided, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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