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Segment Information (Narrative and Major Customers) (Details) (Electric operating revenues [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
First Choice [Member]
Concentration Risk [Line Items]
Operating revenues from continuing operations (as a percent)	15.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_FirstChoiceMember	17.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_FirstChoiceMember
Unaffiliated Customer of Texas-New Mexico Power Company One [Member]
Concentration Risk [Line Items]
Operating revenues from continuing operations (as a percent)	15.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyOneMember	16.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyOneMember	17.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyOneMember
Unaffiliated Customer of Texas-New Mexico Power Company Two [Member]
Concentration Risk [Line Items]
Operating revenues from continuing operations (as a percent)	11.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyTwoMember	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyTwoMember	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyTwoMember
PNMR and PNM [Member] | Maximum [Member]
Concentration Risk [Line Items]
Number of Customers that make up 10 percent of total revenue	0pnm_NumberofCustomersthatmakeup10percentoftotalrevenue / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Operating revenues from continuing operations (as a percent)	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Texas-New Mexico Power Company [Member] | Maximum [Member]
Concentration Risk [Line Items]
Number of Customers that make up 10 percent of total revenue	2pnm_NumberofCustomersthatmakeup10percentoftotalrevenue / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RangeAxis = us-gaap_MaximumMember

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- Definition

Number of Customers that make up 10 percent of total revenue

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: 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=35750535&loc=d3e13537-108611



Reference 2: 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 3: 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=35750535&loc=d3e13531-108611



Reference 4: 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

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