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Commitments and Contingencies - The Clean Air Act (Details) $ in Millions	Dec. 31, 2020 USD ($) lb_PER_MMBTU T	Feb. 21, 2020 USD ($)	Dec. 31, 2018 USD ($) MW	Dec. 31, 2015 MW	Aug. 06, 2012 compliance_alternative	Dec. 31, 1999 state
Public Service Company of New Mexico | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Forecasted undepreciated investment	$ 283.0	$ 361.0
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, 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				132
Pre-tax impairment of investments			$ 35.0
Undepreciated investment in ownership to be obtained			11.9
Forecasted undepreciated investment			$ 23.1
Clean Air Act, SNCR | Public Service Company of New Mexico | San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Additional ownership to be obtained (in megawatts) | MW			132	132
Clean Air Act, SNCR | PNMR Development | San Juan Generating Station Unit 4
Public Utilities, General Disclosures [Line Items]
Potential acquisition of ownership (in megawatts) | MW			65	65
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_PER_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			$ 88.7
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%

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