Benefit Plans and Other Postretirement Benefits (Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		$ 1,142,000	$ 1,067,000	$ 3,426,000	$ 3,203,000
Interest cost		1,918,000	2,007,000	5,753,000	6,023,000
Expected return on plan assets		(2,622,000)	(2,871,000)	(7,867,000)	(8,613,000)
Amortization of prior service cost (credit)		442,000	473,000	1,328,000	1,421,000
Amortization of net loss		1,460,000	1,019,000	4,382,000	3,053,000
Net benefit cost recognized for financial reporting		2,340,000	1,695,000	7,022,000	5,087,000
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	4,000	15,000	13,000
Interest cost		268,000	287,000	806,000	859,000
Expected return on plan assets		(13,000)	(19,000)	(38,000)	(56,000)
Amortization of transition obligation		42,000	42,000	128,000	128,000
Amortization of prior service cost (credit)		(4,000)	(4,000)	(11,000)	(11,000)
Amortization of net loss		123,000	93,000	365,000	275,000
Net benefit cost recognized for financial reporting		421,000	403,000	1,265,000	1,208,000
Xcel Energy Inc. [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