XML 34 R41.htm IDEA: XBRL DOCUMENT v3.20.1
Borrowings and Other Financing Instruments Bilateral Credit Agreement (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Short-term Debt [Line Items]    
Amount outstanding at period end $ 1,765 $ 595
Letter of Credit    
Short-term Debt [Line Items]    
Debt Instrument, Term 1 year  
Amount outstanding at period end $ 20 $ 20
Bilateral Credit Agreement [Member] | NSP Minnesota [Member] | Letter of Credit    
Short-term Debt [Line Items]    
Debt Instrument, Term 1 year  
Credit Facility $ 75  
Amount outstanding at period end 26  
Available $ 49