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Variable Interest Entities (Narrative) (Details)			3 Months Ended			6 Months Ended		12 Months Ended
	May 24, 2024 USD ($)	Mar. 18, 2024 USD ($)	Jun. 30, 2024 USD ($) Rate MW	Mar. 31, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) Rate MW	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Variable Interest Entity [Line Items]
Wind Power Purchase Agreement, Purchase Percentage | Rate			100.00%			100.00%
Payments to Acquire Assets, Investing Activities	$ 114.9	$ 110,600,000
Business Acquisition, Transaction Costs								$ 54,700,000
Proceeds from Contributed Capital				$ 2,160,000,000
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount								1,360,000,000
Income Taxes			$ 17,600,000		$ 14,100,000	$ 93,600,000	$ 99,900,000	$ 63,500,000
Contributions from NIPSCO minority interest holders			59,700,000
Contributions from NIPSCO minority interest holders			$ 20,200,000
Rosewater
Variable Interest Entity [Line Items]
Nameplate Capacity | MW			102			102
Indiana Crossroads Wind
Variable Interest Entity [Line Items]
Nameplate Capacity | MW			302			302
Indiana Crossroads Solar
Variable Interest Entity [Line Items]
Nameplate Capacity | MW			200			200
Dunns Bridge I
Variable Interest Entity [Line Items]
Nameplate Capacity | MW			265			265

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