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CONSOLIDATED STATEMENTS OF CAPITALIZATION (Parenthetical) - $ / shares
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Common Stockholders' Equity    
Common stock, shares authorized (in shares) 1,000,000,000 1,000,000,000
Common stock, par value (in dollars per share) $ 2.50 $ 2.50
Common stock, shares outstanding (in shares) 507,535,523 505,733,267
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2015    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage   1.95%
Debt instrument, maturity date   Aug. 15, 2015
NSP-Minnesota | First Mortgage Bonds | Series Due March 1, 2018    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.25% 5.25%
Debt instrument, maturity date Mar. 01, 2018 Mar. 01, 2018
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2020    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 2.20%  
Debt instrument, maturity date Aug. 15, 2020  
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2022    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 2.15% 2.15%
Debt instrument, maturity date Aug. 15, 2022 Aug. 15, 2022
NSP-Minnesota | First Mortgage Bonds | Series Due May 15, 2023    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 2.60% 2.60%
Debt instrument, maturity date May 15, 2023 May 15, 2023
NSP-Minnesota | First Mortgage Bonds | Series Due July 1, 2025    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 7.125% 7.125%
Debt instrument, maturity date Jul. 01, 2025 Jul. 01, 2025
NSP-Minnesota | First Mortgage Bonds | Series Due March 1, 2028    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.50% 6.50%
Debt instrument, maturity date Mar. 01, 2028 Mar. 01, 2028
NSP-Minnesota | First Mortgage Bonds | Series Due July 15, 2035    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.25% 5.25%
Debt instrument, maturity date Jul. 15, 2035 Jul. 15, 2035
NSP-Minnesota | First Mortgage Bonds | Series Due June 1, 2036    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.25% 6.25%
Debt instrument, maturity date Jun. 01, 2036 Jun. 01, 2036
NSP-Minnesota | First Mortgage Bonds | Series Due July 1, 2037    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.20% 6.20%
Debt instrument, maturity date Jul. 01, 2037 Jul. 01, 2037
NSP-Minnesota | First Mortgage Bonds | Series Due Nov. 1, 2039    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.35% 5.35%
Debt instrument, maturity date Nov. 01, 2039 Nov. 01, 2039
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2040    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.85% 4.85%
Debt instrument, maturity date Aug. 15, 2040 Aug. 15, 2040
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2042    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.40% 3.40%
Debt instrument, maturity date Aug. 15, 2042 Aug. 15, 2042
NSP-Minnesota | First Mortgage Bonds | Series Due May 15, 2044    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.125% 4.125%
Debt instrument, maturity date May 15, 2044 May 15, 2044
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2045    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.00%  
Debt instrument, maturity date Aug. 15, 2045  
PSCo | First Mortgage Bonds | Series Due Sept. 1, 2017    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage [1] 4.375% 4.375%
Debt instrument, maturity date [1] Sep. 01, 2017 Sep. 01, 2017
PSCo | First Mortgage Bonds | Series Due Aug. 1, 2018    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.80% 5.80%
Debt instrument, maturity date Aug. 01, 2018 Aug. 01, 2018
PSCo | First Mortgage Bonds | Series Due June 1, 2019    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.125% 5.125%
Debt instrument, maturity date Jun. 01, 2019 Jun. 01, 2019
PSCo | First Mortgage Bonds | Series Due Nov. 15, 2020    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.20% 3.20%
Debt instrument, maturity date Nov. 15, 2020 Nov. 15, 2020
PSCo | First Mortgage Bonds | Series Due Sept. 15, 2022    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 2.25% 2.25%
Debt instrument, maturity date Sep. 15, 2022 Sep. 15, 2022
PSCo | First Mortgage Bonds | Series Due March 15, 2023    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 2.50% 2.50%
Debt instrument, maturity date Mar. 15, 2023 Mar. 15, 2023
PSCo | First Mortgage Bonds | Series Due May 15, 2025    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 2.90%  
Debt instrument, maturity date May 15, 2025  
PSCo | First Mortgage Bonds | Series Due Sept. 1, 2037    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.25% 6.25%
Debt instrument, maturity date Sep. 01, 2037 Sep. 01, 2037
PSCo | First Mortgage Bonds | Series Due Aug. 1, 2038    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.50% 6.50%
Debt instrument, maturity date Aug. 01, 2038 Aug. 01, 2038
PSCo | First Mortgage Bonds | Series Due Aug. 15, 2041    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.75% 4.75%
Debt instrument, maturity date Aug. 15, 2041 Aug. 15, 2041
PSCo | First Mortgage Bonds | Series Due Sept. 15, 2042    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.60% 3.60%
Debt instrument, maturity date Sep. 15, 2042 Sep. 15, 2042
PSCo | First Mortgage Bonds | Series Due March 15, 2043    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.95% 3.95%
Debt instrument, maturity date Mar. 15, 2043 Mar. 15, 2043
PSCo | First Mortgage Bonds | Series Due March 15, 2044    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.30% 4.30%
Debt instrument, maturity date Mar. 15, 2044 Mar. 15, 2044
PSCo | Capital Lease Obligations    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum 11.20%  
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum 14.30%  
Debt Instrument, Maturity Date Range, End Dec. 31, 2060  
SPS | First Mortgage Bonds | Series Due Aug. 15, 2041    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.50% 4.50%
Debt instrument, maturity date Aug. 15, 2041 Aug. 15, 2041
SPS | First Mortgage Bonds | Series Due June 15, 2024    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.30% 3.30%
Debt instrument, maturity date Jun. 15, 2024 Jun. 15, 2024
SPS | Senior Unsecured Notes | Senior E Due Oct. 1, 2016    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.60% 5.60%
Debt instrument, maturity date Oct. 01, 2016 Oct. 01, 2016
SPS | Senior Unsecured Notes | Senior G Due Dec. 1, 2018    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 8.75% 8.75%
Debt instrument, maturity date Dec. 01, 2018 Dec. 01, 2018
SPS | Senior Unsecured Notes | Senior C and D Due Oct. 1, 2033    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.00% 6.00%
Debt instrument, maturity date Oct. 01, 2033 Oct. 01, 2033
SPS | Senior Unsecured Notes | Senior F Due Oct. 1, 2036    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.00% 6.00%
Debt instrument, maturity date Oct. 01, 2036 Oct. 01, 2036
NSP-Wisconsin | First Mortgage Bonds | Series Due Oct. 1, 2018    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.25% 5.25%
Debt instrument, maturity date Oct. 01, 2018 Oct. 01, 2018
NSP-Wisconsin | First Mortgage Bonds | Series Due June 15, 2024    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.30% 3.30%
Debt instrument, maturity date Jun. 15, 2024 Jun. 15, 2024
NSP-Wisconsin | First Mortgage Bonds | Series Due Sept. 1, 2038    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.375% 6.375%
Debt instrument, maturity date Sep. 01, 2038 Sep. 01, 2038
NSP-Wisconsin | First Mortgage Bonds | Series Due Oct. 1, 2042    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.70% 3.70%
Debt instrument, maturity date Oct. 01, 2042 Oct. 01, 2042
NSP-Wisconsin | City of La Crosse Resource Recovery Bond | Series Due Nov. 1, 2021    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage [2] 6.00% 6.00%
Debt instrument, maturity date [2] Nov. 01, 2021 Nov. 01, 2021
NSP-Wisconsin | Fort McCoy System Acquisition | Due Oct. 15, 2030    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 7.00% 7.00%
Debt instrument, maturity date Oct. 15, 2030 Oct. 15, 2030
Other Subsidiaries | Various Eloigne Co. Affordable Housing Project Notes | Due 2016-2052    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum 0.00%  
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum 8.00%  
Debt Instrument, Maturity Date Range, Start Jan. 01, 2016  
Debt Instrument, Maturity Date Range, End Dec. 31, 2052  
Xcel Energy Inc.    
Common Stockholders' Equity    
Common stock, shares outstanding (in shares) 507,535,523 505,733,267
Xcel Energy Inc. | Senior Unsecured Notes | Series Due May 9, 2016    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 0.75% 0.75%
Debt instrument, maturity date May 09, 2016 May 09, 2016
Xcel Energy Inc. | Senior Unsecured Notes | Series Due April 1, 2017    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 5.613% 5.613%
Debt instrument, maturity date Apr. 01, 2017 Apr. 01, 2017
Xcel Energy Inc. | Senior Unsecured Notes | Series Due June 1, 2017    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 1.20%  
Debt instrument, maturity date Jun. 01, 2017  
Xcel Energy Inc. | Senior Unsecured Notes | Series Due May 15, 2020    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.70% 4.70%
Debt instrument, maturity date May 15, 2020 May 15, 2020
Xcel Energy Inc. | Senior Unsecured Notes | Series Due June 1, 2025    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 3.30%  
Debt instrument, maturity date Jun. 01, 2025  
Xcel Energy Inc. | Senior Unsecured Notes | Series Due July 1, 2036    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 6.50% 6.50%
Debt instrument, maturity date Jul. 01, 2036 Jul. 01, 2036
Xcel Energy Inc. | Senior Unsecured Notes | Series Due Sept. 15, 2041    
Schedule of Capitalization, Long-term Debt [Line Items]    
Debt instrument, interest rate, stated percentage 4.80% 4.80%
Debt instrument, maturity date Sep. 15, 2041 Sep. 15, 2041
[1] Pollution control financing.
[2] Resource recovery financing.