Commitments and Contingencies - The Clean Air Act (Details)					1 Months Ended	12 Months Ended			35 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 16, 2015 USD ($) MWh MW	Jul. 17, 2015	Dec. 20, 2013 USD ($) $ / kw MW	Aug. 31, 2011 generating_unit	Dec. 31, 2017 USD ($) lb / MMBTU generating_unit joint_owner MW	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 31, 2016 USD ($)	Jan. 26, 2016 state	Jul. 31, 2015 MW	Aug. 06, 2012 compliance_alternative	Jul. 31, 2005 T	Dec. 31, 1999 state
Public Utilities, General Disclosures [Line Items]
Plant in service, held for future use, and to be abandoned						$ 7,238,285,000	$ 6,944,534,000
Accumulated depreciation and amortization						2,592,692,000	2,334,938,000
Regulatory disallowances and restructuring costs						27,036,000	15,011,000	$ 167,471,000
Reversal of deferred items related to BART at SJGS						0	0	1,826,000
Regulatory assets						$ 600,672,000	501,223,000
San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Number of other entities (in joint owner) | joint_owner						5
Four Corners
Public Utilities, General Disclosures [Line Items]
Approved lease extension term			25 years
Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Plant in service, held for future use, and to be abandoned						$ 5,501,070,000	5,359,211,000
Accumulated depreciation and amortization						2,029,534,000	1,809,528,000
Regulatory disallowances and restructuring costs						27,036,000	15,011,000	167,471,000
Reversal of deferred items related to BART at SJGS						0	0	1,826,000
Regulatory assets						$ 459,239,000	$ 365,413,000
Power to be sold to third party (in megawatts) | MW						36
Public Service Company of New Mexico | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Number of units (in generating units) | generating_unit						4
Share of costs						46.30%
Public Service Company of New Mexico | San Juan Generating Station | Surface | Loss on long-term purchase commitment
Public Utilities, General Disclosures [Line Items]
Regulatory disallowances and restructuring costs	$ 16,500,000							16,500,000
Estimate of possible loss						$ 100,400,000
Public Service Company of New Mexico | San Juan Generating Station Units 2 and 3
Public Utilities, General Disclosures [Line Items]
Recovery percentage of estimated undepreciated value						50.00%	50.00%
Plant in service, held for future use, and to be abandoned	468,200,000					$ 439,400,000	$ 471,800,000	468,200,000
Accumulated depreciation and amortization	193,300,000					188,300,000	203,900,000	193,300,000
Net undepreciated book value							267,900,000
Construction work in progress	2,200,000							2,200,000
Net book value	$ 277,100,000					251,100,000	139,300,000	277,100,000
Regulatory assets						125,500,000
Reversal of plant write-off						3,000,000
Reversal of recorded loss for other unrecoverable costs						1,000,000
Total reversed losses						$ 4,000,000
Public Service Company of New Mexico | Four Corners
Public Utilities, General Disclosures [Line Items]
Number of units (in generating units) | generating_unit						2
Public Service Company of New Mexico | Four Corners Units 4 and 5 (Coal)
Public Utilities, General Disclosures [Line Items]
Share of costs						13.00%
Plant in service, held for future use, and to be abandoned						$ 204,432,000
Accumulated depreciation and amortization						100,914,000
Construction work in progress						61,755,000
PNMR Development | Energy Equipment
Public Utilities, General Disclosures [Line Items]
Cost of installing equipment						7,600,000
Environmental Protection Agency | Public Service Company of New Mexico | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Number of units (in generating units) | generating_unit					4
Environmental Protection Agency and NMED | Public Service Company of New Mexico | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Period of time to comply after approval					15 months
Clean Air Act related to Regional Haze
Public Utilities, General Disclosures [Line Items]
Number of states to address regional haze | state														50
Potential to emit tons per year of visibility impairing pollution, maximum (in tons) | T													250
Clean Air Act, SCR | Public Service Company of New Mexico | Installation costs including construction management, gross receipts taxes, AFUDC, and other PNM costs | Minimum | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Estimated total capital cost if requirement occurred						824,000,000
Clean Air Act, SCR | Public Service Company of New Mexico | Installation costs including construction management, gross receipts taxes, AFUDC, and other PNM costs | Maximum | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Estimated total capital cost if requirement occurred						$ 910,000,000
Clean Air Act, SNCR | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Number of other entities (in joint owner) | joint_owner						8
Clean Air Act, SNCR | San Juan Generating Station Unit 4 | CALIFORNIA
Public Utilities, General Disclosures [Line Items]
Number of other entities (in joint owner) | joint_owner						3
Clean Air Act, SNCR | Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Estimated costs to remain unrecovered		$ 20,000,000
Regulatory disallowances and restructuring costs								$ 21,600,000
Net expense							3,700,000
Revision of net book value							900,000
Reclamation expense							4,500,000
Clean Air Act, SNCR | Public Service Company of New Mexico | Restructuring costs
Public Utilities, General Disclosures [Line Items]
Net expense							1,700,000
Clean Air Act, SNCR | Public Service Company of New Mexico | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Overall reduction of ownership (in megawatts) | MW				418
Clean Air Act, SNCR | Public Service Company of New Mexico | San Juan Generating Station Units 2 and 3
Public Utilities, General Disclosures [Line Items]
Requested time period to recover retired units NBV		20 years		20 years				20 years
Newly identified replacement solar generation (in megawatts) | MW				40
Current ownership (in megawatts) | MW		418
Recovery percentage of estimated undepreciated value	50.00%	50.00%						50.00%
Estimated undepreciated value	$ 255,300,000							$ 255,300,000
Regulatory disallowances and restructuring costs								127,600,000
Reversal of deferred items related to BART at SJGS								1,800,000
Accumulated plant write-off, disallowance						$ 128,600,000	128,600,000
Clean Air Act, SNCR | Public Service Company of New Mexico | San Juan Generating Station Units 2 and 3 | Increase in coal mine decommissioning liability
Public Utilities, General Disclosures [Line Items]
Regulatory disallowances and restructuring costs								$ 165,700,000
Clean Air Act, SNCR | Public Service Company of New Mexico | Palo Verde Nuclear Generating Station Unit 3
Public Utilities, General Disclosures [Line Items]
Estimated undepreciated value		$ 154,900,000
Clean Air Act, SNCR | Public Service Company of New Mexico | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Additional ownership to be obtained (in megawatts) | MW		65									132
Estimated rate base value		$ 0
Coal-fired generation (in megawatts) | MW		197
Number of megawatt hours of renewable energy certificates to be acquired and retired (in megawatt hours) | MWh		1
Percentage of ownership held by exiting owners						38.80%
Ownership percentage						38.50%
Estimated increase in cost of acquired interest due to plant in service and accumulated depreciation						$ 261,800,000
Clean Air Act, SNCR | Public Service Company of New Mexico | San Juan Generating Station Unit 3
Public Utilities, General Disclosures [Line Items]
Percentage of ownership held by exiting owners						50.00%
Ownership percentage						50.00%
Clean Air Act, SNCR | Public Service Company of New Mexico | Maximum | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Annual cost of renewable energy credits, maximum		$ 7,000,000.0
Clean Air Act, SNCR | Public Service Company of New Mexico | Installation costs including construction management, gross receipts taxes, AFUDC, and other PNM costs | San Juan Generating Station Units 1 and 4
Public Utilities, General Disclosures [Line Items]
Portion of costs for SNCRs and BDT equipment									$ 77,700,000
Clean Air Act, SNCR | Public Service Company of New Mexico | Installation costs including construction management, gross receipts taxes, AFUDC, and other PNM costs | Minimum | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Estimated installation capital costs						$ 85,000,000
Estimated portion of total capital costs if requirement occurred						105,000,000
Clean Air Act, SNCR | Public Service Company of New Mexico | Installation costs including construction management, gross receipts taxes, AFUDC, and other PNM costs | Maximum | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Estimated installation capital costs						90,000,000
Estimated portion of total capital costs if requirement occurred						$ 110,000,000
Clean Air Act, SNCR | Public Service Company of New Mexico | Installation costs including construction management, gross receipts taxes, AFUDC, and other PNM costs | Maximum | San Juan Generating Station Units 1 and 4
Public Utilities, General Disclosures [Line Items]
Estimated installation capital costs				$ 82,000,000
Clean Air Act, SNCR | Public Service Company of New Mexico | Scenario, plan | San Juan Generating Station Units 1 and 4
Public Utilities, General Disclosures [Line Items]
Ownership percentage						66.30%
Clean Air Act, SNCR | Public Service Company of New Mexico | Scenario, plan | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Ownership percentage						77.30%
Clean Air Act, SNCR | PNMR and PNM | Palo Verde Nuclear Generating Station Unit 3
Public Utilities, General Disclosures [Line Items]
Number of megawatts | MW		134		134
Proposed value per kilowatt (in dollars per kilowatt) | $ / kw				2,500
Clean Air Act, SNCR | PNMR Development | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Reimbursement amount							600,000
Potential acquisition of ownership (in megawatts) | MW											65
Restructuring fee							$ 3,100,000
Clean Air Act, SNCR Hearing Examiner Recommended Denial | Public Service Company of New Mexico | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Additional ownership to be obtained (in megawatts) | MW		132
Estimated undepreciated value		$ 20,700,000.0
Clean Air Act, Post-2022 Coal Supply future rate case | Public Service Company of New Mexico | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Period of time for stipulation agreement		6 months
Clean Air Act Related to Post Combustion Controls | Public Service Company of New Mexico | Four Corners
Public Utilities, General Disclosures [Line Items]
Number of compliance alternatives | compliance_alternative												2
Government standard emissions limit (in pounds per MMBTU) | lb / MMBTU						0.015
Plant requirement to meet opacity limit						20.00%
Rule imposes opacity limitation on certain fugitive dust emissions from coal and material handling operations						20.00%
Estimate of possible loss						$ 88,900,000
Clean Air Act Related to Post Combustion Controls | Public Service Company of New Mexico | Four Corners Units 4 and 5 (Coal)
Public Utilities, General Disclosures [Line Items]
Ownership percentage						13.00%
Clean Power Plan
Public Utilities, General Disclosures [Line Items]
Number of states that filed a petition against the Clean Power Plan | state										29