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Revenue Recognition Revenue Recognition (Allowance for Credit Losses) (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Accounts Receivable Allowance For Credit Loss [Line Items] |  |  |
Accounts Receivable, Allowance for Credit Loss | $ 17.7 | $ 22.9 | $ 23.9
Current period provisions | (28.2) | (39.8) |
Write-offs charged against allowance | 43.0 | 61.6 |
Recoveries of amounts previously written off | 9.6 | 20.8 |
Corporate and Other |  |  |
Accounts Receivable Allowance For Credit Loss [Line Items] |  |  |
Accounts Receivable, Allowance for Credit Loss | 0.0 | 0.8 | 0.8
Current period provisions | 0.0 | 0.0 |
Write-offs charged against allowance | (0.8) | 0.0 |
Recoveries of amounts previously written off | 0.0 | 0.0 |
Columbia Operations |  |  |
Accounts Receivable Allowance For Credit Loss [Line Items] |  |  |
Accounts Receivable, Allowance for Credit Loss | 3.7 | 10.2 | 11.1
Current period provisions | (18.9) | (28.3) |
Write-offs charged against allowance | 34.3 | 49.2 |
Recoveries of amounts previously written off | 8.9 | 20.0 |
NIPSCO Operations |  |  |
Accounts Receivable Allowance For Credit Loss [Line Items] |  |  |
Accounts Receivable, Allowance for Credit Loss | 14.0 | 11.9 | $ 12.0
Current period provisions | (9.3) | (11.5) |
Write-offs charged against allowance | 7.9 | 12.4 |
Recoveries of amounts previously written off | $ 0.7 | $ 0.8 |

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