XML 141 R110.htm IDEA: XBRL DOCUMENT v3.8.0.1
Regulatory and Rate Matters - Renewable Energy Rider (Details) - Public Service Company of New Mexico - Renewable energy rider - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Public Utilities, General Disclosures [Line Items]      
Revenue from renewable energy rider $ 45.2 $ 42.0 $ 41.9
Maximum      
Public Utilities, General Disclosures [Line Items]      
Annual revenue to be collected $ 43.5    
NMPRC-approved return on equity 0.50%   10.50%