CONSOLIDATED STATEMENTS OF CAPITALIZATION - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Capitalization, Long-term Debt [Line Items]
Less current maturities	$ 450,000	$ 0
Less current maturities	657,021	257,726
Long-term debt, noncurrent	12,490,719	11,499,634
Common Stockholders' Equity
Common stock — 1,000,000,000 shares authorized of $2.50 par value; 507,535,523 and 505,733,267 shares outstanding at Dec. 31, 2015 and Dec. 31, 2014, respectively	1,268,839	1,264,333
Additional paid in capital	5,889,106	5,837,330
Retained earnings	3,552,728	3,220,958
Accumulated other comprehensive loss	(109,753)	(108,139)
Total common stockholders’ equity	10,600,920	10,214,482
NSP-Minnesota
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(15,911)	(11,365)
Long-term Debt	4,534,122	4,188,682
Less current maturities	11	250,013
Long-term debt, noncurrent	4,534,111	3,938,669
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2015
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	0	250,000
NSP-Minnesota | First Mortgage Bonds | Series Due March 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	500,000	500,000
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	0
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2022
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
NSP-Minnesota | First Mortgage Bonds | Series Due May 15, 2023
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400,000	400,000
NSP-Minnesota | First Mortgage Bonds | Series Due July 1, 2025
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
NSP-Minnesota | First Mortgage Bonds | Series Due March 1, 2028
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	150,000	150,000
NSP-Minnesota | First Mortgage Bonds | Series Due July 15, 2035
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
NSP-Minnesota | First Mortgage Bonds | Series Due June 1, 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400,000	400,000
NSP-Minnesota | First Mortgage Bonds | Series Due July 1, 2037
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	350,000	350,000
NSP-Minnesota | First Mortgage Bonds | Series Due Nov. 1, 2039
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2040
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	500,000	500,000
NSP-Minnesota | First Mortgage Bonds | Series Due May 15, 2044
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2045
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	0
NSP-Minnesota | Other
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	33	47
PSCo
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(11,340)	(11,480)
Total long-term debt	4,132,191	3,890,229
Less current maturities	8,103	8,178
Long-term debt, noncurrent	4,124,088	3,882,051
PSCo | First Mortgage Bonds | Series Due Sept. 1, 2017
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	129,500	129,500
PSCo | First Mortgage Bonds | Series Due Aug. 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
PSCo | First Mortgage Bonds | Series Due June 1, 2019
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400,000	400,000
PSCo | First Mortgage Bonds | Series Due Nov. 15, 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400,000	400,000
PSCo | First Mortgage Bonds | Series Due Sept. 15, 2022
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
PSCo | First Mortgage Bonds | Series Due March 15, 2023
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
PSCo | First Mortgage Bonds | Series Due May 15, 2025
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	0
PSCo | First Mortgage Bonds | Series Due Sept. 1, 2037
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	350,000	350,000
PSCo | First Mortgage Bonds | Series Due Aug. 1, 2038
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
PSCo | First Mortgage Bonds | Series Due Aug. 15, 2041
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
PSCo | First Mortgage Bonds | Series Due Sept. 15, 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	500,000	500,000
PSCo | First Mortgage Bonds | Series Due March 15, 2043
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
PSCo | First Mortgage Bonds | Series Due March 15, 2044
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
PSCo | Capital Lease Obligations
Schedule of Capitalization, Long-term Debt [Line Items]
Capital Lease Obligations	164,031	172,209
SPS
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	605	(309)
Long-term Debt	1,550,605	1,349,691
Less current maturities	200,000	0
Long-term debt, noncurrent	1,350,605	1,349,691
SPS | First Mortgage Bonds | Series Due Aug. 15, 2041
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400,000	400,000
SPS | First Mortgage Bonds | Series Due June 15, 2024
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	350,000	150,000
SPS | Senior Unsecured Notes | Senior E Due Oct. 1, 2016
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	200,000	200,000
SPS | Senior Unsecured Notes | Senior G Due Dec. 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
SPS | Senior Unsecured Notes | Senior C and D Due Oct. 1, 2033
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	100,000	100,000
SPS | Senior Unsecured Notes | Senior F Due Oct. 1, 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
NSP-Wisconsin
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(3,131)	(2,519)
Long-term Debt	667,593	568,291
Less current maturities	1,131	1,235
Long-term debt, noncurrent	666,462	567,056
NSP-Wisconsin | First Mortgage Bonds | Series Due June 15, 2024
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	200,000	100,000
NSP-Wisconsin | First Mortgage Bonds | Series Due Oct. 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	150,000	150,000
NSP-Wisconsin | First Mortgage Bonds | Series Due Sept. 1, 2038
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	200,000	200,000
NSP-Wisconsin | First Mortgage Bonds | Series Due Oct. 1, 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	100,000	100,000
NSP-Wisconsin | City of La Crosse Resource Recovery Bond | Series Due Nov. 1, 2021
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	18,600	18,600
NSP-Wisconsin | Fort McCoy System Acquisition | Due Oct. 15, 2030
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	490	523
NSP-Wisconsin | Other
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	1,634	1,687
Other Subsidiaries
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt	31,255	32,037
Less current maturities	709	1,316
Long-term debt, noncurrent	30,546	30,721
Other Subsidiaries | Various Eloigne Co. Affordable Housing Project Notes | Due 2016-2052
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	31,255	32,037
Xcel Energy Inc.
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(5,551)	(6,078)
Total long-term debt	2,231,974	1,728,431
Less current maturities	447,067	(3,015)
Long-term debt, noncurrent	1,848,428	1,797,901
Long-term debt, noncurrent	1,784,907	1,731,446
Common Stockholders' Equity
Total common stockholders’ equity	10,600,920	10,214,482
Xcel Energy Inc. | Senior Unsecured Notes | Series Due May 9, 2016
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	450,000	450,000
Xcel Energy Inc. | Senior Unsecured Notes | Series Due April 1, 2017
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	253,979	253,979
Xcel Energy Inc. | Senior Unsecured Notes | Series Due June 1, 2017
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	0
Xcel Energy Inc. | Senior Unsecured Notes | Series Due May 15, 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	550,000	550,000
Xcel Energy Inc. | Senior Unsecured Notes | Series Due June 1, 2025
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	0
Xcel Energy Inc. | Senior Unsecured Notes | Series Due July 1, 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300,000	300,000
Xcel Energy Inc. | Senior Unsecured Notes | Series Due Sept. 15, 2041
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250,000	250,000
Xcel Energy Inc. | Capital Lease Obligations
Schedule of Capitalization, Long-term Debt [Line Items]
Capital Lease Obligations	$ (66,454)	$ (69,470)