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Income Taxes - Federal Income Tax Reform (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2023
Dec. 31, 2023
Dec. 31, 2019
Income Taxes [Line Items]      
Federal and state excess deferred income taxes   $ 23.0  
PNM      
Income Taxes [Line Items]      
Federal and state excess deferred income taxes   14.3  
TNMP      
Income Taxes [Line Items]      
Federal and state excess deferred income taxes   $ 8.7  
NMPRC      
Income Taxes [Line Items]      
Proposed term for providing benefits to customers related to reduction in state corporate tax 3 years   23 years