Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Long-Term Borrowings and Other Financing Instruments (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2018
Long-Term Borrowings and Other Financing Instruments
Less current maturities	$ 406.0	$ 457.0
Long-term debt, noncurrent	15,803.0	14,520.0
Amount outstanding at period end	1,038.0	814.0
2019	406.0
2020	1,257.0
2021	425.0
2022	902.0
2023	653.0
Proceeds from issuance of common stock	$ 230.0	0.0	$ 0.0
Forward Equity Agreements [Member]
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Maturity Date	Feb. 07, 2020
Common Stock, Value, to be Issued through Forward Equity Agreement				$ 459.0
Common Stock To Be Issued through forward Equity Agreement				9.4
Period End Settlement Price, In Shares	9.4
Period End Settlement Price, in Cash	$ 456.0
Period End Net Cash Settlement Price	$ 24.0
Period End Net Share Settlement Price	0.5
At-the-Market Offering [Member]
Long-Term Borrowings and Other Financing Instruments
Maximum Aggregate Gross Sales Price of Common Stock that Can Be Offered and Sold	$ 4.7
Proceeds from issuance of common stock	224.7
Transaction fees	1.9
DividendReinvestmentProgram [Member]
Long-Term Borrowings and Other Financing Instruments
Proceeds from issuance of common stock	38.5	39.2
Minimum | Forward Equity Agreements [Member]
Long-Term Borrowings and Other Financing Instruments
expected settlement price	450.0
Maximum | Forward Equity Agreements [Member]
Long-Term Borrowings and Other Financing Instruments
expected settlement price	$ 460.0
Senior Unsecured Notes | Series Due June 15, 2028
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Xcel Energy Inc.
Long-Term Borrowings and Other Financing Instruments
Unamortized discount	$ (5.0)	(2.0)
Unamortized debt expense	(21.0)	(20.0)
Less current maturities	2.0	2.0
Long-term debt, noncurrent	3,316.0	2,818.0
Xcel Energy Inc. | Senior Unsecured Notes
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 3,400.0	$ 2,900.0
Debt Instrument, Maturity Date Range, Start	May 15, 2020
Debt Instrument, Maturity Date Range, End	Sep. 15, 2041
Xcel Energy Inc. | Senior Unsecured Notes | Series Due June 15, 2028
Long-Term Borrowings and Other Financing Instruments
Face Amount	$ 500.0
Debt Instrument, Maturity Date	Jun. 15, 2028
Xcel Energy Inc. | Senior Unsecured Notes | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	2.40%	1.20%
Xcel Energy Inc. | Senior Unsecured Notes | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	6.50%	6.50%
Xcel Energy Inc. | Capital Lease Obligations
Long-Term Borrowings and Other Financing Instruments
Capital Lease Obligations	$ (60.0)	$ (62.0)
Other Subsidiaries
Long-Term Borrowings and Other Financing Instruments
Less current maturities	(1.0)	(2.0)
Long-term debt, noncurrent	25.0	26.0
Other Subsidiaries | Various Eloigne Co. Affordable Housing Project Notes
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 26.0	$ 28.0
Debt Instrument, Maturity Date Range, Start	Sep. 01, 2019
Debt Instrument, Maturity Date Range, End	Dec. 31, 2052
Other Subsidiaries | Various Eloigne Co. Affordable Housing Project Notes | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	0.00%	0.00%
Other Subsidiaries | Various Eloigne Co. Affordable Housing Project Notes | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	6.90%	7.05%
NSP-Minnesota
Long-Term Borrowings and Other Financing Instruments
Unamortized discount	$ (21.0)	$ (22.0)
Unamortized debt expense	(42.0)	(45.0)
Less current maturities	0.0	0.0
Long-term debt, noncurrent	4,937.0	4,933.0
NSP-Minnesota | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 5,000.0	5,000.0
Debt Instrument, Maturity Date Range, Start	Aug. 15, 2020
Debt Instrument, Maturity Date Range, End	Sep. 15, 2047
NSP-Minnesota | First Mortgage Bonds | Series Due Sept. 15, 2047
Long-Term Borrowings and Other Financing Instruments
Face Amount		$ 600.0
Debt Instrument, Interest Rate, Stated Percentage		3.60%
Debt Instrument, Maturity Date		Sep. 15, 2047
NSP-Minnesota | First Mortgage Bonds | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	2.15%	2.15%
NSP-Minnesota | First Mortgage Bonds | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	7.125%	7.125%
NSP-Wisconsin
Long-Term Borrowings and Other Financing Instruments
Unamortized discount	$ (3.0)	$ (3.0)
Unamortized debt expense	(9.0)	(7.0)
Less current maturities	0.0	151.0
Long-term debt, noncurrent	807.0	610.0
NSP-Wisconsin | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 800.0	750.0
Debt Instrument, Maturity Date Range, Start	Jun. 15, 2024
Debt Instrument, Maturity Date Range, End	Sep. 01, 2048
NSP-Wisconsin | First Mortgage Bonds | Series Due September 1, 2048 [Member]
Long-Term Borrowings and Other Financing Instruments
Face Amount	$ 200.0
Debt Instrument, Interest Rate, Stated Percentage	4.20%
Debt Instrument, Maturity Date	Sep. 01, 2048
NSP-Wisconsin | First Mortgage Bonds | Series Due Dec. 1, 2047
Long-Term Borrowings and Other Financing Instruments
Face Amount		$ 100.0
Debt Instrument, Interest Rate, Stated Percentage		3.75%
Debt Instrument, Maturity Date		Dec. 01, 2047
NSP-Wisconsin | First Mortgage Bonds | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	3.30%	3.30%
NSP-Wisconsin | First Mortgage Bonds | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	6.375%	6.375%
NSP-Wisconsin | City of La Crosse Resource Recovery Bond
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 19.0	$ 19.0
Debt Instrument, Interest Rate, Stated Percentage	6.00%	6.00%
Debt Instrument, Maturity Date	Nov. 01, 2021
NSP-Wisconsin | Other
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 0.0	$ 2.0
PSCo
Long-Term Borrowings and Other Financing Instruments
Unamortized discount	(14.0)	(13.0)
Unamortized debt expense	(33.0)	(29.0)
Less current maturities	406.0	306.0
Long-term debt, noncurrent	4,592.0	4,303.0
PSCo | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 4,900.0	4,500.0
Debt Instrument, Maturity Date Range, Start	Jun. 01, 2019
Debt Instrument, Maturity Date Range, End	Jun. 15, 2048
PSCo | First Mortgage Bonds | Series Due June 15, 2028
Long-Term Borrowings and Other Financing Instruments
Face Amount	$ 350.0
Debt Instrument, Interest Rate, Stated Percentage	3.70%
Debt Instrument, Maturity Date	Jun. 15, 2028
PSCo | First Mortgage Bonds | Series Due June 15, 2048
Long-Term Borrowings and Other Financing Instruments
Face Amount	$ 350.0
Debt Instrument, Interest Rate, Stated Percentage	4.10%
Debt Instrument, Maturity Date	Jun. 15, 2048
PSCo | First Mortgage Bonds | Series Due June 15, 2047
Long-Term Borrowings and Other Financing Instruments
Face Amount		$ 400.0
Debt Instrument, Interest Rate, Stated Percentage		3.80%
Debt Instrument, Maturity Date		Jun. 15, 2047
PSCo | First Mortgage Bonds | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	2.25%	2.25%
PSCo | First Mortgage Bonds | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	6.50%	6.50%
PSCo | Capital Lease Obligations
Long-Term Borrowings and Other Financing Instruments
Capital Lease Obligations	$ 145.0	$ 151.0
Debt Instrument, Maturity Date Range, Start	Jan. 01, 2025
Debt Instrument, Maturity Date Range, End	Jan. 01, 2060
PSCo | Capital Lease Obligations | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	11.20%	11.20%
PSCo | Capital Lease Obligations | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	14.30%	14.30%
SPS
Long-Term Borrowings and Other Financing Instruments
Unamortized discount	$ (4.0)	$ (2.0)
Unamortized debt expense	(20.0)	(18.0)
Less current maturities	0.0	0.0
Long-term debt, noncurrent	2,126.0	1,830.0
SPS | Senior Unsecured Notes
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 350.0	$ 350.0
Debt Instrument, Maturity Date Range, Start	Oct. 01, 2033
Debt Instrument, Maturity Date Range, End	Oct. 01, 2036
SPS | Senior Unsecured Notes | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	6.00%	6.00%
SPS | Senior Unsecured Notes | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	6.00%	8.75%
SPS | First Mortgage Bonds
Long-Term Borrowings and Other Financing Instruments
Long-term Debt, Gross	$ 1,800.0	$ 1,500.0
Debt Instrument, Maturity Date Range, Start	Jun. 15, 2024
Debt Instrument, Maturity Date Range, End	Jan. 01, 2048
SPS | First Mortgage Bonds | Series Due June 15, 2048
Long-Term Borrowings and Other Financing Instruments
Face Amount	$ 300.0
Debt Instrument, Interest Rate, Stated Percentage	4.40%
Debt Instrument, Maturity Date	Nov. 15, 2048
SPS | First Mortgage Bonds | Series Due August 15, 2047
Long-Term Borrowings and Other Financing Instruments
Face Amount		$ 450.0
Debt Instrument, Interest Rate, Stated Percentage		3.70%
Debt Instrument, Maturity Date		Aug. 15, 2047
SPS | First Mortgage Bonds | Minimum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	3.30%	3.30%
SPS | First Mortgage Bonds | Maximum
Long-Term Borrowings and Other Financing Instruments
Debt Instrument, Interest Rate, Stated Percentage	4.50%	4.50%