CONSOLIDATED STATEMENTS OF CAPITALIZATION (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Long-Term Debt
Long-term debt, current maturities	$ 1,059,922		$ 55,415
Long-term debt, noncurrent	8,848,513		9,263,144
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		104,980
Common Stockholders' Equity
Common Stock - authorized 1,000,000,000 shares of $2.50 par value; 486,493,933 and 482,333,750 shares outstanding at Dec. 31, 2011 and 2010, respectively	1,216,234		1,205,834
Additional paid in capital	5,327,443		5,229,075
Retained earnings	2,032,556		1,701,703
Accumulated other comprehensive loss	(94,035)		(53,093)
Total common stockholders' equity	8,482,198		8,083,519
Preferred Stock $3.60 Series [Member]
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		27,500
Preferred Stock $4.08 Series [Member]
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		15,000
Preferred Stock $4.10 Series [Member]
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		17,500
Preferred Stock $4.11 Series [Member]
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		20,000
Preferred Stock $4.16 Series [Member]
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		9,980
Preferred Stock $4.56 Series [Member]
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		15,000
NSP-Minnesota [Member]
Long-Term Debt
Unamortized discount	(8,011)		(9,020)
Total long-term debt	3,338,897		3,337,912
Long-term debt, current maturities	450,000		19
Long-term debt, noncurrent	2,888,897		3,337,893
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due Aug. 28, 2012 [Member]
Long-Term Debt
Long-term debt, gross	450,000		450,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due Aug. 15, 2015 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due March 1, 2018 [Member]
Long-Term Debt
Long-term debt, gross	500,000		500,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due March 1, 2019 [Member]
Long-Term Debt
Long-term debt, gross	27,900	[1]	27,900	[1]
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due Sept. 1, 2019 [Member]
Long-Term Debt
Long-term debt, gross	100,000	[1]	100,000	[1]
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due July 1, 2025 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due March 1, 2028 [Member]
Long-Term Debt
Long-term debt, gross	150,000		150,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due April 1, 2030 [Member]
Long-Term Debt
Long-term debt, gross	69,000	[1]	69,000	[1]
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due July 15, 2035 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due June 1, 2036 [Member]
Long-Term Debt
Long-term debt, gross	400,000		400,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due July 1, 2037 [Member]
Long-Term Debt
Long-term debt, gross	350,000		350,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due Nov. 1, 2039 [Member]
Long-Term Debt
Long-term debt, gross	300,000		300,000
NSP-Minnesota [Member] | First Mortgage Bonds [Member] | Series Due Aug. 15, 2040 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
NSP-Minnesota [Member] | Other [Member]
Long-Term Debt
Long-term debt, gross	8		32
PSCo [Member]
Long-Term Debt
Unamortized discount	(8,349)		(8,250)
Total long-term debt	3,486,275		3,235,223
Long-term debt, current maturities	605,633		6,970
Long-term debt, noncurrent	2,880,642		3,228,253
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Oct. 1, 2012 [Member]
Long-Term Debt
Long-term debt, gross	600,000		600,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due March 1, 2013 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due April 1, 2014 [Member]
Long-Term Debt
Long-term debt, gross	275,000		275,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Sept. 1, 2017 [Member]
Long-Term Debt
Long-term debt, gross	129,500	[1]	129,500	[1]
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Aug. 1, 2018 [Member]
Long-Term Debt
Long-term debt, gross	300,000		300,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Jan. 1, 2019 [Member]
Long-Term Debt
Long-term debt, gross	48,750	[1]	48,750	[1]
PSCo [Member] | First Mortgage Bonds [Member] | Series Due June 1, 2019 [Member]
Long-Term Debt
Long-term debt, gross	400,000		400,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Nov. 15, 2020 [Member]
Long-Term Debt
Long-term debt, gross	400,000		400,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Sept. 1, 2037 [Member]
Long-Term Debt
Long-term debt, gross	350,000		350,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Aug. 1, 2038 [Member]
Long-Term Debt
Long-term debt, gross	300,000		300,000
PSCo [Member] | First Mortgage Bonds [Member] | Series Due Aug. 15, 2041 [Member]
Long-Term Debt
Long-term debt, gross	250,000		0
PSCo [Member] | Capital Lease Obligations [Member]
Long-Term Debt
Capital lease obligations	191,374		190,223
SPS [Member]
Long-Term Debt
Unamortized discount	(6,686)		(4,033)
Total long-term debt	993,314		897,767
Long-term debt, current maturities	0		44,500
Long-term debt, noncurrent	993,314		853,267
SPS [Member] | First Mortgage Bonds [Member] | Series Due Aug. 15, 2041 [Member]
Long-Term Debt
Long-term debt, gross	200,000		0
SPS [Member] | Unsecured Senior Notes [Member] | Senior E Due Oct. 1, 2016 [Member]
Long-Term Debt
Long-term debt, gross	200,000		200,000
SPS [Member] | Unsecured Senior Notes [Member] | Senior G Due Dec. 1, 2018 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
SPS [Member] | Unsecured Senior Notes [Member] | Senior C and D Due Oct. 1, 2033 [Member]
Long-Term Debt
Long-term debt, gross	100,000		100,000
SPS [Member] | Unsecured Senior Notes [Member] | Senior F Due Oct. 1, 2036 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
SPS [Member] | Pollution Control Obligations, Securing Pollution Control Revenue Bonds [Member] | Due July 1, 2011 [Member]
Long-Term Debt
Long-term debt, gross	0		44,500
SPS [Member] | Pollution Control Obligations, Securing Pollution Control Revenue Bonds [Member] | Due Sept. 1, 2016 [Member]
Long-Term Debt
Long-term debt, gross	0		57,300
NSP-Wisconsin [Member]
Long-Term Debt
Unamortized discount	(1,748)		(1,857)
Total long-term debt	369,369		369,356
Long-term debt, current maturities	1,286		1,502
Long-term debt, noncurrent	368,083		367,854
NSP-Wisconsin [Member] | First Mortgage Bonds [Member] | Series Due Oct. 1, 2018 [Member]
Long-Term Debt
Long-term debt, gross	150,000		150,000
NSP-Wisconsin [Member] | First Mortgage Bonds [Member] | Series Due Sept. 1, 2038 [Member]
Long-Term Debt
Long-term debt, gross	200,000		200,000
NSP-Wisconsin [Member] | City of La Crosse Resource Recovery Bond [Member] | Series Due Nov. 1, 2021 [Member]
Long-Term Debt
Long-term debt, gross	18,600	[2]	18,600	[2]
NSP-Wisconsin [Member] | Fort McCoy System Acquisition [Member] | Due Oct. 15, 2030 [Member]
Long-Term Debt
Long-term debt, gross	625		659
NSP-Wisconsin [Member] | Other [Member]
Long-Term Debt
Long-term debt, gross	1,892		1,954
Other Subsidiaries [Member]
Long-Term Debt
Total long-term debt	53,728		61,039
Long-term debt, current maturities	4,974		5,088
Long-term debt, noncurrent	48,754		55,951
Other Subsidiaries [Member] | Various Eloigne Co. Affordable Housing Project Notes [Member] | Due 2012-2045 [Member]
Long-Term Debt
Long-term debt, gross	53,728		61,039
Xcel Energy Inc. [Member]
Long-Term Debt
Unamortized discount	(10,798)		(11,780)
Total long-term debt	1,666,852		1,417,262
Long-term debt, current maturities	(1,971)		(2,664)
Long-term debt, noncurrent	1,668,823		1,419,926
Preferred Stock - authorized 7,000,000 shares of $100 par value; outstanding shares: 2011: 0; 2010: 1,049,800
Preferred stock	0		104,980
Common Stockholders' Equity
Total common stockholders' equity	8,482,198		8,083,519
Xcel Energy Inc. [Member] | Unsecured Senior Notes [Member] | Series Due April 1, 2017 [Member]
Long-Term Debt
Long-term debt, gross	253,979		253,979
Xcel Energy Inc. [Member] | Unsecured Senior Notes [Member] | Series Due May 15, 2020 [Member]
Long-Term Debt
Long-term debt, gross	550,000		550,000
Xcel Energy Inc. [Member] | Unsecured Senior Notes [Member] | Series Due July 1, 2036 [Member]
Long-Term Debt
Long-term debt, gross	300,000		300,000
Xcel Energy Inc. [Member] | Unsecured Senior Notes [Member] | Series Due Sept. 15, 2041 [Member]
Long-Term Debt
Long-term debt, gross	250,000		0
Xcel Energy Inc. [Member] | Junior Subordinated Notes [Member] | Series Due Jan. 1, 2068 [Member]
Long-Term Debt
Long-term debt, gross	400,000		400,000
Xcel Energy Inc. [Member] | Capital Lease Obligations [Member]
Long-Term Debt
Capital lease obligations	$ (76,329)		$ (74,937)

[1] Pollution control financing.

[2] Resource recovery financing.