Income Taxes (Details) (USD $) In Millions, unless otherwise specified			6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 State Jurisdiction [Member]	Jun. 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				2007
Earliest year subject to examination			2006	2008
Year(s) under examination			None	None
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit - Permanent tax positions	$ 0.5	$ 0.5
Unrecognized tax benefit - Temporary tax positions	10.1	10.9
Unrecognized tax benefit balance	10.6	11.4
NOL and tax credit carryforwards	(3.2)	(3.7)
Amounts accrued for penalties related to unrecognized tax benefits	$ 0	$ 0