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Borrowings and Other Financing Instruments - Letters of Credit (Details) - USD ($)
3 Months Ended
Mar. 31, 2024
Dec. 31, 2023
Line of Credit Facility [Line Items]    
Short-term debt $ 145,000,000 $ 75,000,000
Letter of Credit    
Line of Credit Facility [Line Items]    
Debt Instrument, Term 1 year  
Revolving Credit Facility [Member]    
Line of Credit Facility [Line Items]    
Direct advances on the credit facility outstanding $ 0 0
Letter of Credit    
Line of Credit Facility [Line Items]    
Direct advances on the credit facility outstanding   $ 0