Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2017
Income Tax Contingency [Line Items]
Effective tax rate	14.64%
Income tax assessment	$ 0.2
Deferred federal, state and local, income taxes	$ 23.3
PNM
Income Tax Contingency [Line Items]
Effective tax rate	13.09%
Income tax assessment	$ 0.1
Deferred federal, state and local, income taxes	$ 20.7
TNMP
Income Tax Contingency [Line Items]
Effective tax rate	20.72%
Income tax assessment	$ 0.1
Deferred federal, state and local, income taxes	$ 2.6
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	5 years	23 years
Unprotected excess deferred income taxes	$ 62.7