Income Taxes (Details) (USD $) In Millions, unless otherwise specified			9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 State Jurisdiction [Member]	Sep. 30, 2012 Xcel Energy Inc. [Member] Internal Revenue Service (IRS) [Member]
Income Tax Examination [Line Items]
Year(s) no longer subject to audit as statute of limitations has expired				2008
Earliest year subject to examination			2007	2009
Year(s) under examination			None	2010 and 2011
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit - Permanent tax positions	$ 0.2	$ 0.2
Unrecognized tax benefit - Temporary tax positions	4.8	4.6
Total unrecognized tax benefit	5.0	4.8
NOL and tax credit carryforwards	(2.1)	(2.0)
Amounts accrued for penalties related to unrecognized tax benefits	$ 0	$ 0