Jointly-Owned Electric Generating Plants (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
Jun. 30, 2011 Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member]	Jun. 30, 2011 Public Service Company of New Mexico [Member] Four Corners [Member] Beginning 2016 [Member]	Jun. 30, 2011 Jointly Owned Nuclear Power Plant [Member]
Jointly Owned Utility Plant Interests [Line Items]
Operating Lease, Original Term			40 years
Operating Lease, Extended Term			20 years
Increase (Decrease) in Asset Retirement Obligations	$ 4.2
Jointly Owned Utility, Lease Payment		$ 0.9

Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 143
-Paragraph 22
-Subparagraph c(4)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Name:	us-gaap_AssetRetirementObligationRevisionOfEstimate
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration