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Regulatory and Rate Matters - Four Corners Abandonment Application (Narrative) (Details) - Four Corners - PNM - USD ($)
$ in Millions
 1 Months Ended 9 Months Ended
Jan. 08, 2021
Nov. 01, 2020
Aug. 31, 2024
Nov. 30, 2020
Sep. 30, 2023
Public Utilities, General Disclosures [Line Items]          
Payments for relief from obligations   $ 75.0   $ 15.0  
Final payment for relief from obligations       $ 60.0  
Request issuance of energy transition bonds $ 300.0        
Regulatory disallowance         $ 3.7
Reimbursement agreement payment     $ 15.0    
PNM          
Public Utilities, General Disclosures [Line Items]          
Ownership percentage by noncontrolling owners   13.00%