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Variable Interest Entities (Schedule of Cash Contributions) (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Cash Contributions Noncontrolling Interest [Line Items] |  |  |
Obligation to the Developer | $ 0.0 | $ 0.0 | $ 277.5
Consolidated Variable Interest Entities |  |  |
Cash Contributions Noncontrolling Interest [Line Items] |  |  |
NIPSCO's Cash Contribution | 401.5 |  |
Tax Equity Partners Cash Contribution | $ 507.2 |  |
Obligation to the Developer |  | $ 347.2 |

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- Details
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