XML 55 R41.htm IDEA: XBRL DOCUMENT v3.24.1.u1
Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($)
$ in Millions
Mar. 31, 2024
Dec. 31, 2023
Regulatory Assets and Liabilities [Line Items]    
Total Current Regulatory Assets $ 8.7 $ 9.3
Total Non-Current Regulatory Assets 409.0 425.4
Total Current Regulatory Liabilities 17.1 3.9
Total Non-Current Regulatory Liabilities 564.0 574.0
Fuel Adjustment Clause    
Regulatory Assets and Liabilities [Line Items]    
Total Current Regulatory Liabilities 9.0 0.0
Total Non-Current Regulatory Liabilities 8.2 15.5
Provision for Interim Rate Refund    
Regulatory Assets and Liabilities [Line Items]    
Total Current Regulatory Liabilities 5.5 0.0
Transmission Formula Rates Refund    
Regulatory Assets and Liabilities [Line Items]    
Total Current Regulatory Liabilities 1.0 1.5
Other    
Regulatory Assets and Liabilities [Line Items]    
Total Current Regulatory Liabilities 1.6 2.4
Total Non-Current Regulatory Liabilities 6.1 4.4
Income Taxes    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Liabilities 302.3 310.0
Wholesale and Retail Contra AFUDC    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Liabilities 77.3 78.0
Plant Removal Obligations    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Liabilities 69.3 67.0
Defined Benefit Pension and Other Postretirement Benefit Plans    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Liabilities 45.5 48.6
Non-Jurisdictional Land Sales    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Liabilities 35.1 30.2
Investment Tax Credits    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Liabilities 13.5 13.6
Boswell Units 1 and 2 Net Plant and Equipment    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Liabilities 6.7 6.7
Fuel Adjustment Clause    
Regulatory Assets and Liabilities [Line Items]    
Total Current Regulatory Assets 8.1 8.7
Total Non-Current Regulatory Assets 2.1 5.0
Other    
Regulatory Assets and Liabilities [Line Items]    
Total Current Regulatory Assets 0.6 0.6
Total Non-Current Regulatory Assets 3.3 4.2
Defined Benefit Pension and Other Postretirement Benefit Plans    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Assets 217.3 218.6
Income Taxes    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Assets 85.1 88.1
Asset Retirement Obligations    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Assets 38.3 37.7
Cost Recovery Riders    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Assets 27.6 33.8
Taconite Harbor    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Assets 18.3 20.9
Manufactured Gas Plant    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Assets 13.1 13.2
PPACA Income Tax Deferral    
Regulatory Assets and Liabilities [Line Items]    
Total Non-Current Regulatory Assets $ 3.9 $ 3.9