Commitments and Contingencies - Stipulation Filed with the NMPRC (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended
	Apr. 08, 2015	Oct. 01, 2014	Dec. 20, 2013	Mar. 31, 2015 MW	Jan. 15, 2015 MW	Jun. 26, 2014 MW
San Juan Generating Station Unit 4 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Additional Ownership To Be Obtained, in Megawatts		132	78	132		132
Public Utilities, Estimated rate base value at 1/1/2018		$ 26.0
Public Utilities, Ownership in Megawatts PNM has agreed not to obtain					65
San Juan Generating Station Unit 4 [Member] | Subsequent Event [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR Hearing Examiner Recommended Denial [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Additional Ownership To Be Obtained, in Megawatts	132
Period of time to accept or reject modifications in recommendation	7 days
San Juan Generating Station Unit 3 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Proposed reduction in carrying value		26
Public Utilities,Estimated unrecoverable increase in operations and maintenance		20
San Juan Generating Station Unit 3 [Member] | Maximum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities,Estimated pre-tax regulatory disallowance		70
San Juan Generating Station Unit 3 [Member] | Minimum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities,Estimated pre-tax regulatory disallowance		60
San Juan Generating Station Unit 3 [Member] | Subsequent Event [Member] | Maximum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities,Estimated pre-tax regulatory disallowance	155
San Juan Generating Station Unit 3 [Member] | Subsequent Event [Member] | Minimum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities,Estimated pre-tax regulatory disallowance	145
San Juan Generating Station Units 2 and 3 [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Net book value				280
San Juan Generating Station Units 2 and 3 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Recovery Percentage of Estimated undepreciated value at 12/31/17		50.00%
Public Utilities, Estimated undepreciated value at 12/31/17		231.0
Public Utilities, Requested Time Period to Recover Retired Units NBV		20 years	20 years
Public Utilities, Write-off Percentage of Estimated undepreciated value at 12/31/17		50.00%
San Juan Generating Station Units 2 and 3 [Member] | Subsequent Event [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Estimated undepreciated value at 12/31/17	128.5
Public Utilities, Write-off Percentage of Estimated undepreciated value at 12/31/17	50.00%
Palo Verde Nuclear Generating Station Unit 3 [Member] | Public Service Company of New Mexico [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Net book value				145
Palo Verde Nuclear Generating Station Unit 3 [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Estimated rate base value at 1/1/2018		221.1
Public Utilities, Proposed value per Kilowatt effective January 1, 2018		1,650
Palo Verde Nuclear Generating Station Unit 3 [Member] | PNMR and PNM [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Number of Megawatts Nuclear Generation				134
Palo Verde Nuclear Generating Station Unit 3 [Member] | PNMR and PNM [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Number of Megawatts Nuclear Generation		134	134
Public Utilities, Proposed value per Kilowatt effective January 1, 2018			2,500
Public Utilities, Percentage capacity factor 7-year performance threshold		75.00%
Public Utilities, Period over which to measure capacity performance		7 years
Palo Verde Nuclear Generating Station Unit 3 [Member] | Subsequent Event [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR Hearing Examiner Recommended Denial [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Public Utilities, Estimated rate base value at 1/1/2018	143.5
Public Utilities, Proposed value per Kilowatt effective January 1, 2018	1,071
San Juan Generating Station Units 1 and 4 [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] | Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Estimated Installation Capital Costs		$ 90.6	82.0