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Operations and Significant Accounting Policies - Other Non-Current Liabilities (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Business Segments [Line Items]    
Asset Retirement Obligation $ 202.9 $ 200.4
PSAs 20.9 26.9
Other 40.5 41.7
Total Other Non-Current Liabilities 264.3 269.0
BNI Energy    
Business Segments [Line Items]    
Other receivables $ 37.2 $ 32.4