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Commitments and Contingencies NSP-Minnesota-Sherco (Details) - USD ($)
$ in Millions
 1 Months Ended 9 Months Ended
Jan. 31, 2021
Sep. 30, 2024
May 17, 2024
Rate Matters [Abstract]      
Sherco Disallowance $ 22    
ALJ Recommended Customer Refund     $ 34
Disallowance Not Considered in ALJ Recommendation     $ 22
2011 Sherco Unit 3 Outage Refunds   $ 46  
NSP-Minnesota      
Rate Matters [Abstract]      
Customer refund of previously recovered purchased power costs $ 17