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Commitments and Contingencies - Four Corners (Details) $ in Millions	Sep. 30, 2015 USD ($) lbsofnox / mmbtu	Dec. 31, 2013	Aug. 06, 2012 compliance_alternative
Four Corners [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public utilities, jointly owned utility plant, sale of ownership percentage		48.00%
Clean Air Act Related to Post Combustion Controls [Member] | Public Service Company of New Mexico [Member] | Four Corners [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public utilities, number of compliance alternatives			2
Public utilities, plant requirement to meet NOx emissions limit (in pounds of NOx per MMBTU) | lbsofnox / mmbtu	0.015
Public utilities, plant requirement to meet opacity limit	20.00%
Public utilities, rule imposes opacity limitation on certain fugitive dust emissions from coal and material handling operations	20.00%
Loss contingency, estimate of possible loss | $	$ 91.4
Clean Air Act Related to Post Combustion Controls [Member] | Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public utilities, ownership percentage	13.00%

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Public Utilities, Rule Imposes Opacity Limitation on Certain Fugitive Dust Emissions From Coal and Material Handling Operations

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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



-Publisher FASB



-Name Accounting Standards Codification



-Topic 450



-SubTopic 20



-Section 50



-Paragraph 4



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-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349



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



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-Name Accounting Standards Codification



-Topic 450



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