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Variable Interest Entities (Narrative) (Details) $ in Millions				3 Months Ended
	Mar. 31, 2025 USD ($) Rate MW	Feb. 03, 2025 USD ($)	Jan. 15, 2025 USD ($)	Mar. 31, 2025 USD ($) Rate MW	Mar. 31, 2024 USD ($)
Variable Interest Entity [Line Items]
Wind Power Purchase Agreement, Purchase Percentage | Rate	100.00%			100.00%
Payments to Acquire Assets, Investing Activities | $	$ 144.1	$ 217.6	$ 336.6
Income Taxes | $				$ 105.7	$ 76.0
Contributions from NIPSCO minority interest holders | $				34.8
Payments to Noncontrolling Interests | $				$ 17.5	$ 0.0
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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