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		$ 2,127,000	$ 1,896,000	$ 4,260,000	$ 3,845,000
Interest cost		4,920,000	5,087,000	9,800,000	10,018,000
Expected return on plan assets		(6,217,000)	(6,559,000)	(12,464,000)	(13,158,000)
Amortization of prior service cost (credit)		359,000	377,000	719,000	753,000
Amortization of net loss		3,265,000	2,576,000	6,407,000	4,523,000
Net periodic benefit cost		4,454,000	3,377,000	8,722,000	5,981,000
Cost not recognized due to the effects of regulation		(1,075,000)	(575,000)	(2,150,000)	(1,150,000)
Net benefit cost recognized for financial reporting		3,379,000	2,802,000	6,572,000	4,831,000
Pension contributions attributable to SPS	12,900,000
Postretirement Health Care Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		302,000	254,000	630,000	546,000
Interest cost		745,000	684,000	1,416,000	1,361,000
Expected return on plan assets		(674,000)	(754,000)	(1,351,000)	(1,503,000)
Amortization of transition obligation		387,000	418,000	773,000	835,000
Amortization of prior service cost (credit)		(37,000)	(13,000)	(74,000)	(26,000)
Amortization of net loss		345,000	216,000	628,000	428,000
Net periodic benefit cost		1,068,000	805,000	2,022,000	1,641,000
Net benefit cost recognized for financial reporting		1,068,000	805,000	2,022,000	1,641,000
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