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Pension and Other Postretirement Benefit Plans Narrative (Details) (USD $) | 12 Months Ended |  | 12 Months Ended | 0 Months Ended | 12 Months Ended
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Dec. 31, 2011 | Jan. 30, 2009 | Dec. 31, 2011 Pension Plan [Member] | Dec. 31, 2011 Other Postretirement Benefits [Member] | Dec. 31, 2009 PNM Gas [Member] | Dec. 31, 2011 Public Service Company of New Mexico [Member] Pension Plan [Member] | Dec. 31, 2010 Public Service Company of New Mexico [Member] Pension Plan [Member] | Dec. 31, 2011 Public Service Company of New Mexico [Member] Other Postretirement Benefits [Member] | Dec. 31, 2010 Public Service Company of New Mexico [Member] Other Postretirement Benefits [Member] | Jan. 30, 2009 Public Service Company of New Mexico [Member] PNM Gas [Member] Other Postretirement Benefits [Member] | Dec. 31, 2011 Texas-New Mexico Power Company [Member] Pension Plan [Member] | Dec. 31, 2010 Texas-New Mexico Power Company [Member] Pension Plan [Member] | Dec. 31, 2011 Texas-New Mexico Power Company [Member] Other Postretirement Benefits [Member] | Dec. 31, 2010 Texas-New Mexico Power Company [Member] Other Postretirement Benefits [Member] | Dec. 31, 2011 Equity Securities [Member] Pension Plan [Member] | Dec. 31, 2011 Equity Securities [Member] Other Postretirement Benefits [Member] | Dec. 31, 2011 Debt Securities [Member] Pension Plan [Member] | Dec. 31, 2011 Debt Securities [Member] Other Postretirement Benefits [Member] | Dec. 31, 2011 Alternative Investments [Member] Pension Plan [Member] | Dec. 31, 2011 Developed Countries Outside of United States [Member] Equity Securities [Member] Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Election of relieving losses in asset market value (in years) | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans, Gains and losses that lie outside the corridor, amortized (in years) | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Benefit obligation, period increase (decrease) |  |  |  |  |  | $ (2,800,000) | $ (41,500,000) | $ (7,400,000) | $ 20,100,000 |  | $ 1,200,000 | $ (5,100,000) |  |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease) Due to Change in Demographics |  |  |  |  |  |  | 9,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Actuarial net (gains) losses |  |  |  |  | 9,600,000 | (1,197,000) | (51,379,000) | (712,000) | 17,952,000 |  | 2,793,000 | (5,113,000) | 862,000 | 116,000 |  |  |  |  |  |
Actual plan asset allocations (as a percent) |  |  |  |  |  | 8.00% |  | 3.80% |  |  | 7.70% |  | 3.20% |  |  |  |  |  |  |
Expected long-term return resulting from effect of one-percentage point decrease (as a percent) |  |  | 1.00% | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected Long-term return on assets decrease resulting in increase net periodic costs In next fiscal year |  |  |  |  |  | 5,000,000 |  | 600,000 |  |  | 600,000 |  | 100,000 |  |  |  |  |  |  |
Expected long-term return resulting from effect of one-percentage point increase (as a percent) |  |  | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Target plan asset allocations (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 42.00% | 70.00% | 41.00% | 30.00% | 17.00% | 10.00%
Estimated future employer contributions in next fiscal year |  |  |  |  |  | 77,700,000 |  | 2,500,000 |  |  | 5,300,000 |  | 200,000 |  |  |  |  |  |  |
Estimated future employer contributions from 2012-2016 |  |  |  |  |  | 85,300,000 |  |  |  |  | 1,800,000 |  |  |  |  |  |  |  |  |
Weighted average discount rate related to anticipated contributions (as a percent) |  |  | 5.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability transfer resulting from sale |  | 15,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net unamortized (gain) loss arising during period, net of tax |  |  |  |  |  |  |  |  |  | $ 2,900,000 |  |  |  |  |  |  |  |  |  |

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- Definition The net increase or decrease of changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=6514294 -Topic 715 -SubTopic 30 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph a -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=6749293 -Topic 715 -SubTopic 60 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 106 -Paragraph 518 -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 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 264 -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. + Details
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- Definition Net increase or decrease in the plan benefit obligation during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph a -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 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 + Details
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- Definition The employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph g -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 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 + Details
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- Definition The aggregate percentage of the fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of total plan assets held as of the measurement date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph d(1) -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 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2446-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 + Details
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- Definition The accumulated change in the value of either the projected benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption that has not been recognized in net periodic benefit cost, after tax. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6920433&loc=d3e998-108581 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 158 -Paragraph 4 -Subparagraph c, d -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 17, 19, 24 -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 158 -Paragraph 7 -Subparagraph a -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 5: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph c(3) -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 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e653-108580 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e637-108580 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 + Details
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