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Borrowings and Other Financing Instruments - Letters of Credit (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2023
Dec. 31, 2022
Line of Credit Facility [Line Items]    
Term of letters of credit (in years) 1 year  
Short-term debt $ 0 $ 294
Letter of Credit    
Line of Credit Facility [Line Items]    
Short-term debt $ 29 $ 27
Letter of Credit | Letter of Credit    
Line of Credit Facility [Line Items]    
Term of letters of credit (in years) 1 year