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		$ 21,853,000	$ 20,548,000	$ 43,182,000	$ 38,660,000
Interest cost		39,365,000	40,791,000	78,088,000	80,706,000
Expected return on plan assets		(52,072,000)	(55,514,000)	(103,548,000)	(110,800,000)
Amortization of prior service cost (credit)		5,267,000	5,633,000	10,533,000	11,266,000
Amortization of net loss		27,467,000	20,527,000	53,785,000	39,256,000
Net periodic benefit cost		41,880,000	31,985,000	82,040,000	59,088,000
Cost not recognized and additional cost recognized due to the effects of regulation		(10,158,000)	(10,715,000)	(19,291,000)	(18,600,000)
Net benefit cost recognized for financial reporting		31,722,000	21,270,000	62,749,000	40,488,000
Total contributions to Xcel Energy's pension plans during the period	190,500,000
Number of pension plans to which contributions were made	4
Postretirement Health Care Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		922,000	1,097,000	2,102,000	2,412,000
Interest cost		9,551,000	10,492,000	18,931,000	21,043,000
Expected return on plan assets		(7,094,000)	(8,013,000)	(14,205,000)	(15,981,000)
Amortization of transition obligation		3,580,000	3,611,000	7,160,000	7,222,000
Amortization of prior service cost (credit)		(1,888,000)	(1,233,000)	(3,776,000)	(2,466,000)
Amortization of net loss		4,487,000	3,304,000	8,452,000	6,647,000
Net periodic benefit cost		9,558,000	9,258,000	18,664,000	18,877,000
Cost not recognized and additional cost recognized due to the effects of regulation		973,000	973,000	1,946,000	1,946,000
Net benefit cost recognized for financial reporting		$ 10,531,000	$ 10,231,000	$ 20,610,000	$ 20,823,000