CONSOLIDATED STATEMENTS OF CAPITALIZATION - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Capitalization, Long-term Debt [Line Items]
Less current maturities	$ 457	$ 255
Long-term debt, noncurrent	14,520	14,195
Common Stockholders' Equity
Common stock — 1,000,000,000 shares authorized of $2.50 par value; 507,762,881 and 507,222,795 shares outstanding at Dec. 31, 2017 and 2016, respectively	1,269	1,268
Additional paid in capital	5,898	5,881
Retained earnings	4,413	3,982
Accumulated other comprehensive loss	(125)	(110)
Total common stockholders’ equity	11,455	11,021
Other Subsidiaries
Schedule of Capitalization, Long-term Debt [Line Items]
Less current maturities	2	1
Long-term debt, noncurrent	26	30
Other Subsidiaries | Various Eloigne Co. Affordable Housing Project Notes | Due 2018-2052
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	28	31
Xcel Energy Inc.
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(2)	(2)
Unamortized debt expense	(20)	(23)
Total long-term debt	2,816	3,061
Less current maturities	0	250
Less current maturities	(2)	248
Long-term debt, noncurrent	2,878	2,875
Long-term debt, noncurrent	2,818	2,813
Common Stockholders' Equity
Total common stockholders’ equity	11,455	11,021
Xcel Energy Inc. | Senior Unsecured Notes | Series Due June 1, 2017
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	0	250
Xcel Energy Inc. | Senior Unsecured Notes | Series Due May 15, 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	550	550
Xcel Energy Inc. | Senior Unsecured Notes | Series Due March 15, 2021
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400	400
Xcel Energy Inc. | Senior Unsecured Notes | Series Due March 15, 2022
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
Xcel Energy Inc. | Senior Unsecured Notes | Series Due June 1, 2025
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	600	600
Xcel Energy Inc. | Senior Unsecured Notes | Series Due Dec. 1, 2026
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	500	500
Xcel Energy Inc. | Senior Unsecured Notes | Series Due July 1, 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
Xcel Energy Inc. | Senior Unsecured Notes | Series Due Sept. 15, 2041
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
Xcel Energy Inc. | Capital Lease Obligations
Schedule of Capitalization, Long-term Debt [Line Items]
Capital Lease Obligations	(62)	(64)
NSP-Minnesota
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(22)	(17)
Unamortized debt expense	(45)	(40)
Long-term debt, noncurrent	4,933	4,843
NSP-Minnesota | First Mortgage Bonds | Series Due March 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	0	500
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2022
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
NSP-Minnesota | First Mortgage Bonds | Series Due May 15, 2023
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400	400
NSP-Minnesota | First Mortgage Bonds | Series Due July 1, 2025
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
NSP-Minnesota | First Mortgage Bonds | Series Due March 1, 2028
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	150	150
NSP-Minnesota | First Mortgage Bonds | Series Due July 15, 2035
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
NSP-Minnesota | First Mortgage Bonds | Series Due June 1, 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400	400
NSP-Minnesota | First Mortgage Bonds | Series Due July 1, 2037
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	350	350
NSP-Minnesota | First Mortgage Bonds | Series Due Nov. 1, 2039
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2040
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	500	500
NSP-Minnesota | First Mortgage Bonds | Series Due May 15, 2044
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
NSP-Minnesota | First Mortgage Bonds | Series Due Aug. 15, 2045
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
NSP-Minnesota | First Mortgage Bonds | Series Due May 15, 2046
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	350	350
NSP-Minnesota | First Mortgage Bonds | Series Due Sept. 15, 2047
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	600	0
PSCo
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(13)	(13)
Unamortized debt expense	(29)	(27)
Total long-term debt	4,609	4,216
Less current maturities	306	5
Long-term debt, noncurrent	4,303	4,211
PSCo | First Mortgage Bonds | Series Due Aug. 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
PSCo | First Mortgage Bonds | Series Due June 1, 2019
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400	400
PSCo | First Mortgage Bonds | Series Due Nov. 15, 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400	400
PSCo | First Mortgage Bonds | Series Due Sept. 15, 2022
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
PSCo | First Mortgage Bonds | Series Due March 15, 2023
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
PSCo | First Mortgage Bonds | Series Due May 15, 2025
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
PSCo | First Mortgage Bonds | Series Due Sept. 1, 2037
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	350	350
PSCo | First Mortgage Bonds | Series Due Aug. 1, 2038
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
PSCo | First Mortgage Bonds | Series Due Aug. 15, 2041
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
PSCo | First Mortgage Bonds | Series Due Sept. 15, 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	500	500
PSCo | First Mortgage Bonds | Series Due March 15, 2043
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
PSCo | First Mortgage Bonds | Series Due March 15, 2044
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
PSCo | First Mortgage Bonds | Series Due June 15, 2046
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
PSCo | First Mortgage Bonds | Series Due June 15, 2047
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400	0
PSCo | Capital Lease Obligations
Schedule of Capitalization, Long-term Debt [Line Items]
Capital Lease Obligations	151	156
SPS
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(2)	0
Unamortized debt expense	(18)	(14)
Long-term debt, noncurrent	1,830	1,636
SPS | First Mortgage Bonds | Series Due Aug. 15, 2041
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	400	400
SPS | First Mortgage Bonds | Series Due June 15, 2024
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	350	350
SPS | First Mortgage Bonds | Series Due Aug. 15, 2046
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	300	300
SPS | First Mortgage Bonds | Series Due Aug. 15, 2047
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	450	0
SPS | Senior Unsecured Notes | Senior G Due Dec. 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	0	250
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	100
SPS | Senior Unsecured Notes | Senior F Due Oct. 1, 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	250	250
NSP-Wisconsin
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(3)	(3)
Unamortized debt expense	(7)	(5)
Long-term Debt	761	663
Less current maturities	151	1
Long-term debt, noncurrent	610	662
NSP-Wisconsin | First Mortgage Bonds | Series Due June 15, 2024
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	200	200
NSP-Wisconsin | First Mortgage Bonds | Series Due Oct. 1, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	150	150
NSP-Wisconsin | First Mortgage Bonds | Series Due Sept. 1, 2038
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	200	200
NSP-Wisconsin | First Mortgage Bonds | Series Due Oct. 1, 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	100	100
NSP-Wisconsin | First Mortgage Bonds | Series Due Dec. 1, 2047
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	100	0
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	19	19
NSP-Wisconsin | Other
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 2	$ 2