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Borrowings and Other Financing Instruments Term Loan (Details) - USD ($)
9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Mar. 23, 2020
Dec. 31, 2019
Dec. 20, 2019
Short-term Debt [Line Items]          
Amount outstanding at period end $ 500,000,000     $ 595,000,000  
Proceeds from issuance of common stock 5,000,000 $ 457,000,000      
Expiration Period, Line of Credit     $ 364   $ 364
364-Day Term Loan [Member] | Short-term Debt [Member] | Xcel Energy Inc.          
Short-term Debt [Line Items]          
Credit Facility 500,000,000   $ 700,000,000   $ 500,000,000
Required debt to total capitalization ratio     65.00%    
Basis points     50.0    
Amount outstanding at period end 500,000,000        
Available $ 0