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Operations and Significant Accounting Policies - Other Non-Current Liabilities (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Business Segments [Line Items] |  |
Asset Retirement Obligation | $ 206.1 | $ 202.9
PSAs | 19.5 | 20.9
Operating Lease Liabilities | 8.3 | 7.7
Finance Lease Liabilities | 1.5 | 1.6
Other | 32.6 | 31.2
Other Non-Current Liabilities | 268.0 | 264.3
BNI Energy |  |
Business Segments [Line Items] |  |
Other Receivables | $ 37.2 | $ 37.2

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