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		$ 5,679,000	$ 4,432,000	$ 17,039,000	$ 13,295,000
Interest cost		12,776,000	13,059,000	38,329,000	39,176,000
Expected return on plan assets		(16,326,000)	(16,988,000)	(48,977,000)	(50,961,000)
Amortization of prior service cost (credit)		57,000	56,000	171,000	167,000
Amortization of net loss		8,552,000	7,032,000	25,652,000	21,095,000
Net periodic benefit cost		10,738,000	7,591,000	32,214,000	22,772,000
Net benefit cost recognized for financial reporting		10,738,000	7,591,000	32,214,000	22,772,000
Pension contributions attributable to PSCo	41,000,000
Postretirement Health Care Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		706,000	906,000	2,119,000	2,719,000
Interest cost		6,131,000	7,097,000	18,395,000	21,293,000
Expected return on plan assets		(6,264,000)	(6,990,000)	(18,792,000)	(20,971,000)
Amortization of transition obligation		2,751,000	2,751,000	8,253,000	8,253,000
Amortization of prior service cost (credit)		(1,288,000)	(728,000)	(3,863,000)	(2,185,000)
Amortization of net loss		2,734,000	2,236,000	8,198,000	6,707,000
Net periodic benefit cost		4,770,000	5,272,000	14,310,000	15,816,000
Additional cost recognized due to the effects of regulation		972,000	972,000	2,918,000	2,918,000
Net benefit cost recognized for financial reporting		5,742,000	6,244,000	17,228,000	18,734,000
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