Benefit Plans and Other Postretirement Benefits (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		$ 1,150,000	$ 1,234,000	$ 2,284,000	$ 2,136,000
Interest cost		1,925,000	1,998,000	3,835,000	4,016,000
Expected return on plan assets		(2,634,000)	(2,841,000)	(5,245,000)	(5,742,000)
Amortization of prior service cost (credit)		443,000	474,000	886,000	948,000
Amortization of net loss		1,487,000	1,066,000	2,922,000	2,034,000
Net benefit cost recognized for financial reporting		2,371,000	1,931,000	4,682,000	3,392,000
Pension contributions attributable to NSP-Wisconsin	12,300,000
Postretirement Health Care Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		5,000	5,000	10,000	9,000
Interest cost		274,000	300,000	538,000	572,000
Expected return on plan assets		(12,000)	(18,000)	(25,000)	(37,000)
Amortization of transition obligation		43,000	43,000	86,000	86,000
Amortization of prior service cost (credit)		(3,000)	(3,000)	(7,000)	(7,000)
Amortization of net loss		128,000	94,000	242,000	182,000
Net benefit cost recognized for financial reporting		435,000	421,000	844,000	805,000
Xcel Energy Inc. [Member] | Pension Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Total contributions to Xcel Energy's pension plans during the period	$ 190,500,000
Number of Xcel Energy's pension plans to which contributions were made	4