Borrowings and Other Financing Instruments (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended	1 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended		1 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2012		Dec. 31, 2011	Jul. 31, 2012 Xcel Energy Inc. [Member]	Jun. 30, 2012 Xcel Energy Inc. [Member]		Jul. 31, 2012 PSCo [Member]	Jun. 30, 2012 PSCo [Member]		Jul. 31, 2012 NSP-Minnesota [Member]	Jun. 30, 2012 NSP-Minnesota [Member]		Jul. 31, 2012 SPS [Member]	Jun. 30, 2012 SPS [Member]		Jun. 30, 2012 SPS [Member] First Mortgage Bonds [Member] Series Due Aug. 15, 2041 [Member]	Aug. 31, 2011 SPS [Member] First Mortgage Bonds [Member] Series Due Aug. 15, 2041 [Member]	Jul. 31, 2012 NSP-Wisconsin [Member]	Jun. 30, 2012 NSP-Wisconsin [Member]
Commercial Paper [Abstract]
Borrowing limit	$ 2,450,000,000		$ 2,450,000,000		$ 2,450,000,000
Amount outstanding at period end	481,000,000		481,000,000		219,000,000
Average amount outstanding	456,000,000				430,000,000
Maximum amount outstanding	634,000,000				824,000,000
Weighted average interest rate, computed on a daily basis (in hundredths)	0.37%				0.36%
Weighted average interest rate at period end (in hundredths)	0.35%		0.35%		0.40%
Committed Credit Facilities [Abstract]
Credit facility	2,450,000,000		2,450,000,000				800,000,000			700,000,000			500,000,000			300,000,000					150,000,000
Drawn	492,700,000	[1]	492,700,000	[1]			397,000,000	[1]		8,000,000	[1]		8,700,000	[1]		0	[1]				79,000,000	[1]
Available	1,957,300,000		1,957,300,000				403,000,000			692,000,000			491,300,000			300,000,000					71,000,000
Credit facility bank borrowings outstanding	0		0		0
Amended Credit Agreements [Abstract]
Amended term (in years)						5Y			5Y			5Y			5Y					5Y
Original term (in years)							4Y			4Y			4Y			4Y					4Y
Minimum borrowing margin based on long-term credit ratings (in hundredths)						0.875%	1.00%		0.875%	1.00%		0.875%	1.00%		0.875%	1.00%				0.875%	1.00%
Maximum borrowing margin based on long-term credit ratings (in hundredths)						1.75%	2.00%		1.75%	2.00%		1.75%	2.00%		1.75%	2.00%				1.75%	2.00%
Minimum commitment fees calculated on unused portion of lines of credit (in hundredths)						0.075%	0.10%		0.075%	0.10%		0.075%	0.10%		0.075%	0.10%				0.075%	0.10%
Maximum commitment fees calculated on unused portion of lines of credit (in hundredths)						0.275%	0.35%		0.275%	0.35%		0.275%	0.35%		0.275%	0.35%				0.275%	0.35%
Number of additional periods the revolving termination date can be extended, subject to majority bank group approval						2			2			2			2					1
Term of each additional period the revolving termination date can be extended, subject to majority bank group approval (in years)						1Y			1Y			1Y			1Y					1Y
Letters of Credit [Abstract]
Terms of letters of credit (in years)			1Y
Letters of credit outstanding under credit facilities	11,700,000		11,700,000		12,700,000
Letters of credit outstanding not issued under credit facilities	1,100,000		1,100,000		1,100,000
Long-Term Borrowings [Abstract]
Face amount																		100,000,000	200,000,000
Interest rate, stated percentage (in hundredths)																		4.50%	4.50%
Maturity date																		Aug. 15, 2041	Aug. 15, 2041
Unamortized premium																		10,100,000
Principal outstanding																		$ 300,000,000

[1] Includes outstanding commercial paper and letters of credit.