Borrowings and Other Financing Instruments (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Commercial Paper [Abstract]
Borrowing limit	$ 2,450,000,000		$ 2,450,000,000
Amount outstanding at period end	339,000,000		219,000,000
Average amount outstanding	324,000,000		430,000,000
Maximum amount outstanding	463,000,000		824,000,000
Weighted average interest rate, computed on a daily basis (in hundredths)	0.36%		0.36%
Weighted average interest rate at period end (in hundredths)	0.36%		0.40%
Committed Credit Facilities [Abstract]
Credit facility	2,450,000,000
Drawn	349,700,000	[1]
Available	2,100,300,000
Credit facility bank borrowings outstanding	0		0
Letters of Credit [Abstract]
Terms of letters of credit (in years)	1Y
Letters of credit outstanding under credit facilities	10,700,000		12,700,000
Letters of credit outstanding not issued under credit facilities	1,100,000		1,100,000
Xcel Energy Inc. [Member]
Committed Credit Facilities [Abstract]
Credit facility	800,000,000
Drawn	214,000,000	[1]
Available	586,000,000
PSCo [Member]
Committed Credit Facilities [Abstract]
Credit facility	700,000,000
Drawn	3,000,000	[1]
Available	697,000,000
NSP-Minnesota [Member]
Committed Credit Facilities [Abstract]
Credit facility	500,000,000
Drawn	35,700,000	[1]
Available	464,300,000
SPS [Member]
Committed Credit Facilities [Abstract]
Credit facility	300,000,000
Drawn	26,000,000	[1]
Available	274,000,000
NSP-Wisconsin [Member]
Committed Credit Facilities [Abstract]
Credit facility	150,000,000
Drawn	71,000,000	[1]
Available	$ 79,000,000

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