Regulatory and Rate Matters - Energy Efficiency and Load Management (Details) $ in Millions			12 Months Ended
	Apr. 15, 2020 USD ($) MMBTU meter	Jul. 26, 2017 USD ($) GWh	Dec. 31, 2019 USD ($) GWh	Dec. 31, 2018 USD ($)	Nov. 08, 2017	Nov. 07, 2017
Public Service Company of New Mexico | Energy Efficiency and Load Management Program, Proposed 2018 Portfolio | Disincentives/Incentives Added
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency				$ 23.6
Targeted energy savings (in Gigawatts) | GWh		69
Projected earned incentive		$ 1.9	$ 2.7
Energy and load management programs, additional incentive, targeted energy savings (in Gigawatts) | GWh			68
Public Service Company of New Mexico | Energy Efficiency and Load Management Program, Proposed 2019 Portfolio | Disincentives/Incentives Added
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency			$ 24.9
Application of incentive based on target savings		$ 1.7	$ 1.8
Public Service Company of New Mexico | 2017 Energy Efficiency and Load Management Program | Disincentives/Incentives Added
Public Utilities, General Disclosures [Line Items]
Targeted energy savings (in Gigawatts) | GWh			59
Minimum profit incentive			$ 1.8
Public Service Company of New Mexico | Energy Efficiency and Load Management Program
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency, next fiscal year	$ 31.4
Program costs related to energy efficiency, in year two	31.0
Program costs related to energy efficiency, in year three	$ 29.6
Energy efficiency and load management programs targeted energy savings (in Gigawatts) | MMBTU	80
Number of AMI meters to be installed | meter	5,000
Program costs related to meter installation	$ 2.9
Public Service Company of New Mexico | Minimum | Renewable Portfolio Standard
Public Utilities, General Disclosures [Line Items]
Sliding scale profit incentive			7.10%
Profit incentive sliding scale multiplier	0.071
Energy efficiency and load management programs targeted energy savings (in Gigawatts) | MMBTU	80
Measurement Input, Discount Rate
Public Utilities, General Disclosures [Line Items]
Tax-adjusted WACC					0.0959	0.0771