XML 81 R62.htm IDEA: XBRL DOCUMENT v3.10.0.1
Regulatory and Rate Matters - TNMP Narrative (Details)
 1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
May 30, 2018
USD ($)
Jul. 30, 2011
USD ($)
Jun. 30, 2018
USD ($)
advanced_meter
customer
Jun. 30, 2018
USD ($)
advanced_meter
customer
Dec. 31, 2017
USD ($)
Jul. 25, 2018
customer
Public Utilities, Commitments And Contingencies [Line Items]            
Unrecovered investment revenue $ 21,800,000          
TNMP            
Public Utilities, Commitments And Contingencies [Line Items]            
Net regulatory liability         $ 14,400,000  
Reduction to revenue     $ 1,200,000 $ 2,700,000    
Energy efficiency cost recovery, requested change amount 5,700,000          
Energy efficiency cost recovery, requested bonus 900,000   $ 800,000 $ 800,000    
TNMP | 2018 TNMP Rate Case            
Public Utilities, Commitments And Contingencies [Line Items]            
Requested rate increase (decrease) $ 25,900,000          
Requested return on equity 10.50%          
New rate rider recovery, amount $ 7,700,000          
Regulatory liabilities         $ 146,500,000  
TNMP | Advanced Meter System Deployment and Surcharge Request            
Public Utilities, Commitments And Contingencies [Line Items]            
Approved deployment costs   $ 113,400,000        
Collection of deployment costs through surcharge period   12 years        
Number of advanced meters installed (more than) | advanced_meter     242,000 242,000    
Recovery in cost through initial fees     $ 200,000 $ 200,000    
Ongoing annual expenses     500,000 500,000    
Approved non-standard metering ongoing expenses monthly charge     $ 36.78 $ 36.78    
Presumed number of customers that will elect non-standard meter service (in customers) | customer     1,081 1,081    
Minimum | TNMP | Advanced Meter System Deployment and Surcharge Request            
Public Utilities, Commitments And Contingencies [Line Items]            
Approved non-standard metering service cost, initial fee range     $ 63.97 $ 63.97    
Maximum | TNMP | Advanced Meter System Deployment and Surcharge Request            
Public Utilities, Commitments And Contingencies [Line Items]            
Approved non-standard metering service cost, initial fee range     $ 168.61 $ 168.61    
Subsequent event | TNMP | Advanced Meter System Deployment and Surcharge Request            
Public Utilities, Commitments And Contingencies [Line Items]            
Current number of customers that have elected non-standard meter service (in customers) | customer           97