For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Segment Information (Narrative and Major Customers) (Details) (Sales [Member])	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
First Choice [Member]
Concentration Risk [Line Items]
Operating revenues from continuing operations (as a percent)	19.00%	17.00%	18.00%
Unaffiliated Customer of Texas-New Mexico Power Company One [Member]
Concentration Risk [Line Items]
Operating revenues from continuing operations (as a percent)	17.00%	19.00%	19.00%
Unaffiliated Customer of Texas-New Mexico Power Company Two [Member]
Concentration Risk [Line Items]
Operating revenues from continuing operations (as a percent)	10.00%	12.00%	13.00%
PNMR and PNM [Member] \| Maximum [Member]
Concentration Risk [Line Items]
Operating revenues from continuing operations (as a percent)	10.00%