Income Taxes (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2017	Dec. 31, 2020
Income Tax Contingency [Line Items]
Accelerated refund application amount of AMT tax, CARES act						$ 5.2
Deferred tax assets, tax deferred expense, payroll taxes, CARES Act						$ 7.0
Refund amount of AMT tax, CARES act		$ 5.2
Payment of payroll taxes, CARES Act	$ 3.5
Deferred federal, state and local, income taxes				$ 23.6
Effective tax rate			13.12%
PNM
Income Tax Contingency [Line Items]
Deferred federal, state and local, income taxes				14.4
Effective tax rate			14.50%
TNMP
Income Tax Contingency [Line Items]
Deferred federal, state and local, income taxes				$ 9.2
Effective tax rate			12.37%
NMPRC
Income Tax Contingency [Line Items]
Period of time for proposed return to customers the benefit of the reduction in federal corporate income tax rate					23 years
Period of time for proposed return to customers the benefit of the reduction in New Mexico's corporate income tax rate					3 years