Borrowings and Other Financing Instruments (Tables)
 9 Months Ended
Sep. 30, 2012
Borrowings and Other Financing Instruments [Abstract]  
Committed Credit Facility Available
At Sept. 30, 2012, SPS had the following committed credit facility available (in millions of dollars):

Credit Facility
  
Drawn
  
Available
 
$300.0  $-  $300.0 
Commercial Paper [Member]
  
Borrowings and Other Financing Instruments [Abstract]  
Short-Term Debt
Commercial Paper — SPS meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility. The following table presents commercial paper outstanding for SPS:

(Amounts in Millions, Except Interest Rates)
 
Three Months Ended
Sept. 30, 2012
  
Twelve Months Ended
Dec. 31, 2011
 
Borrowing limit
 $300  $300 
Amount outstanding at period end
  -   - 
Average amount outstanding
  -   54 
Maximum amount outstanding
  16   161 
Weighted average interest rate, computed on a daily basis
  0.33%  0.37%
Weighted average interest rate at period end
  N/A   N/A 
Money Pool [Member]
  
Borrowings and Other Financing Instruments [Abstract]  
Short-Term Debt
Money Pool — Xcel Energy Inc. and its utility subsidiaries have established a money pool arrangement that allows for short-term investments in and borrowings between the utility subsidiaries. Xcel Energy Inc. may make investments in the utility subsidiaries at market-based interest rates; however, the utility money pool arrangement does not allow the utility subsidiaries to make investments in Xcel Energy Inc. The following table presents the money pool borrowings for SPS:

(Amounts in Millions, Except Interest Rates)
 
Three Months Ended
Sept. 30, 2012
  
Twelve Months Ended
Dec. 31, 2011
 
Borrowing limit
 $100  $100 
Amount outstanding at period end
  -   5 
Average amount outstanding
  -   12 
Maximum amount outstanding
  9   71 
Weighted average interest rate, computed on a daily basis
  0.33%  0.35%
Weighted average interest rate at period end
  N/A   0.35