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Benefit Plans and Other Postretirement Benefits, Pension Benefits (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Pension Plans [Member]
     
Pension Benefits [Abstract]      
Total benefit obligation $ 454,184 $ 403,367 $ 370,587
Net benefit cost recognized for financial reporting 13,324 9,661 5,793
Expected average long-term rate of return on assets (in hundredths) 6.68% 6.80% 6.80%
Expected average long-term rate of return on assets for next fiscal year (in hundredths) 6.49%    
Target Pension Asset Allocations [Abstract]      
Domestic and international equity securities (in hundredths) 21.00% 20.00%  
Long-duration fixed income securities (in hundredths) 50.00% 50.00%  
Short-to-intermediate fixed income securities (in hundredths) 8.00% 9.00%  
Alternative investments (in hundredths) 19.00% 18.00%  
Cash (in hundredths) 2.00% 3.00%  
Total (in hundredths) 100.00% 100.00%  
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan [Member]
     
Pension Benefits [Abstract]      
Total benefit obligation 3,300 3,300  
Net benefit cost recognized for financial reporting 300 300  
Minimum number of years historical achieved weighted average annual returns are used to determine overall expected return on asset portfolio (in years) 20 years    
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan [Member] | Xcel Energy Inc. [Member]
     
Pension Benefits [Abstract]      
Total benefit obligation 39,400 54,800  
Net benefit cost recognized for financial reporting $ 15,600 $ 5,700