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Rate Matters - West Companies (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended
Apr. 27, 2017
Mar. 31, 2017
Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]      
Construction Work in Progress   $ 3,196.8 $ 3,183.9
Public Service Co Of Oklahoma [Member]      
Public Utilities, General Disclosures [Line Items]      
Construction Work in Progress   106.3 148.2
Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Construction Work in Progress   125.2 $ 113.8
AEP Texas Interim Transmission and Distribution Rates [Member]      
Public Utilities, General Disclosures [Line Items]      
AEP Texas Cumulative Revenues Subject to Review   $ 581.0  
ETT Interim Transmission Rates [Member]      
Public Utilities, General Disclosures [Line Items]      
Parent Ownership Interest In ETT   50.00%  
AEP Share Of ETT Cumulative Revenues Subject To Review   $ 636.0  
Louisiana 2015 Formula Rate Filing [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   14.0  
Louisiana 2015 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   $ 14.0  
Louisiana Turk Plant Prudence Review [Member]      
Public Utilities, General Disclosures [Line Items]      
Louisiana Jurisdictional Share of the Turk Plant   29.00%  
Louisiana Turk Plant Prudence Review [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Louisiana Jurisdictional Share of the Turk Plant   29.00%  
Welsh Plant, Units 1 and 3 - Environmental Projects [Member]      
Public Utilities, General Disclosures [Line Items]      
Projected Capital Costs   $ 850.0  
Construction Work in Progress   398.0  
Remaining Contractual Construction Obligations   10.0  
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs   79.0  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals   11.0  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity   6.0  
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Projected Capital Costs   850.0  
Construction Work in Progress   398.0  
Remaining Contractual Construction Obligations   10.0  
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs   79.0  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals   11.0  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity   6.0  
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Welsh Plant, Units 1 and 3 [Member]      
Public Utilities, General Disclosures [Line Items]      
Property, Plant and Equipment, Net   630.0  
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Welsh Plant, Units 1 and 3 [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Property, Plant and Equipment, Net   630.0  
2012 Texas Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
2013 Reversal of Previously Recorded Regulatory Disallowances   114.0  
Resulting Approved Base Rate Increase   52.0  
2012 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
2013 Reversal of Previously Recorded Regulatory Disallowances   114.0  
Resulting Approved Base Rate Increase   52.0  
2016 Texas Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Net Increase in Texas Annual Revenues   $ 69.0  
Requested Return on Common Equity   10.00%  
Amount Of Increase Related To Environmental Controls   $ 34.0  
Amount of Increase Related to Additonal Investment and Increased Operating Costs   25.0  
Amount of Increase Related to Transmission Cost Recovery   8.0  
Amount of Increase Related to Vegetation Management   $ 2.0  
Texas Jurisdictional Share of the Welsh Plant   33.00%  
2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Net Increase in Texas Annual Revenues   $ 69.0  
Requested Return on Common Equity   10.00%  
Amount Of Increase Related To Environmental Controls   $ 34.0  
Amount of Increase Related to Additonal Investment and Increased Operating Costs   25.0  
Amount of Increase Related to Transmission Cost Recovery   8.0  
Amount of Increase Related to Vegetation Management   $ 2.0  
Texas Jurisdictional Share of the Welsh Plant   33.00%  
Subsequent Event [Member] | Louisiana 2017 Formula Rate Filing [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase $ 36.0    
Subsequent Event [Member] | Louisiana 2017 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase 36.0    
Subsequent Event [Member] | 2016 Texas Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
Recommended Net Increase in Texas Annual Revenues 44.0    
Recommended Investment Disallowances Resulting in Possible Write-Offs 84.0    
Subsequent Event [Member] | 2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Recommended Net Increase in Texas Annual Revenues 44.0    
Recommended Investment Disallowances Resulting in Possible Write-Offs $ 84.0    
Subsequent Event [Member] | Minimum [Member] | 2016 Texas Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
Recommended Return on Equity 9.20%    
Subsequent Event [Member] | Minimum [Member] | 2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Recommended Return on Equity 9.20%    
Subsequent Event [Member] | Maximum [Member] | 2016 Texas Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
Recommended Return on Equity 9.35%    
Subsequent Event [Member] | Maximum [Member] | 2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Recommended Return on Equity 9.35%