Commitments and Contingencies - The Clean Air Act (Details)				3 Months Ended			6 Months Ended		12 Months Ended	40 Months Ended
	Feb. 25, 2016	Dec. 16, 2015 USD ($) MWh MW	Mar. 02, 2015 lb / MMBTU T	Jun. 30, 2016 USD ($) MW	Mar. 31, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) MW	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2016 USD ($) MW	Feb. 09, 2016	Jan. 26, 2016 state	Oct. 01, 2015 parts_per_billion	Sep. 30, 2015 parts_per_billion	Jul. 31, 2015 MW	Dec. 30, 2013 lbsofnox / mmbtu	Aug. 06, 2012 compliance_alternative	Jan. 31, 2010 parts_per_billion	Jul. 31, 2005 T	Dec. 31, 1999 state
Public Utilities, Commitments And Contingencies [Line Items]
Regulatory disallowances and restructuring costs				$ 0		$ 1,529,000	$ 774,000	$ 1,744,000
Plant in service, held for future use, and to be abandoned				6,774,773,000			6,774,773,000		$ 6,307,261,000	$ 6,774,773,000
Accumulated depreciation and amortization				2,279,853,000			2,279,853,000		2,058,772,000	2,279,853,000
Public Service Company of New Mexico [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Regulatory disallowances and restructuring costs				0		$ 1,529,000	774,000	$ 1,744,000
Plant in service, held for future use, and to be abandoned				5,258,713,000			5,258,713,000		4,833,303,000	5,258,713,000
Accumulated depreciation and amortization				1,765,392,000			1,765,392,000		1,569,549,000	1,765,392,000
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Plant in service, held for future use, and to be abandoned				471,500,000			471,500,000			471,500,000
Accumulated depreciation and amortization				199,300,000			199,300,000			199,300,000
Net book value				272,200,000			272,200,000			272,200,000
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Loss on long-term purchase commitment [Member] | Surface [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Regulatory disallowances and restructuring costs									$ 16,500,000
Loss contingency, estimate of possible loss				$ 96,700,000			$ 96,700,000			$ 96,700,000
Public Service Company of New Mexico [Member] | San Juan Generating Station And Four Corners [Member] | Maximum [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Proposed government standard emission limit (in ozone parts per million) | parts_per_billion																		70
Government standard emission limit (in ozone parts per million) | parts_per_billion													70	75
Public Service Company of New Mexico [Member] | San Juan Generating Station And Four Corners [Member] | Minimum [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Proposed government standard emission limit (in ozone parts per million) | parts_per_billion																		60
PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Number of megawatts | MW				134			134			134
Clean Air Act related to Regional Haze [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Number of states to address regional haze (in states) | state																				50
Potential to emit tons per year of visibility impairing pollution (in tons, more than) | T																			250
Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Number of other owner				8			8			8
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Estimated costs to remain unrecovered		$ 20,000,000
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Units 1 and 4 [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Total costs for equipment										$ 76,800,000
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Current ownership interest (in megawatts) | MW		418
Time period to recover retired units' remaining net book value		20 years							20 years
Recovery percentage of estimated undepreciated value at 12/31/17		50.00%		50.00%			50.00%		50.00%	50.00%
Estimated undepreciated value at 12/31/17									$ 255,300,000
Regulatory disallowances and restructuring costs									127,600,000
Expense reflected in regulatory disallowances and restructuring costs					$ 800,000
Accumulated plant write-off, disallowance				$ 128,200,000			$ 128,200,000			$ 128,200,000
Net carrying value of utility plant				144,000,000			144,000,000			144,000,000
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] | Increase in coal mine decommissioning liability [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Regulatory disallowances and restructuring costs									$ 165,700,000
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member]
Public Utilities, Commitments And Contingencies [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
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] | Maximum [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Annual cost of Renewable Energy Credits		$ 7,000,000
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Estimated undepreciated value at 12/31/17		$ 150,000,000
Clean Air Act, SNCR [Member] | PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Number of megawatts | MW		134
Clean Air Act, SNCR [Member] | PNMR Development [Member] | San Juan Generating Station Unit 4 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Expense for cost, obligation to reimburse					$ 600,000
Potential acquisition of ownership (in megawatts) | MW															65
Clean Air Act, SNCR Hearing Examiner Recommended Denial [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Additional ownership to be obtained (in megawatts) | MW		132
Clean Air Act, Post-2022 Coal Supply future rate case [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Period of time agreed to by all parties to settle rate case		6 months
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]
Number of compliance alternatives | compliance_alternative																	2
Plant requirement to meet NOx emissions limit (in pounds of NOx per MMBTU) | lbsofnox / 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%
Loss contingency, estimate of possible loss				$ 91,100,000			$ 91,100,000			$ 91,100,000
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]
Ownership percentage																13.00%
Clean Power Plan [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Period of potential extension to meet environmental targets							2 years
Number of states that filed a petition against the Clean Power Plan | state												29
Proposed percentage reduction in CO2 emissions, stayed by the USSC											32.00%
Period of time currently remaining to submit initial plans to meet environmental targets							6 months
Period of time currently remaining to submit initial plans to meet environmental targets, including potential extension							2 years 6 months
National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Period of time to act on settlement			16 months
Emissions tons of SO2 per year (more than) | T			16,000
National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member] | Public Service Company of New Mexico [Member] | Minimum [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Emissions tons of SO2 per year (more than) | T			2,600
Public utilities, 1-hour SO2 emissions rate (in pounds per MMBTU) | lb / MMBTU			0.45
National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member] [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Period of time from state designation, to provide implementation plans	36 months