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Rate Matters - West Companies (Details) - USD ($)
$ in Thousands
1 Months Ended 12 Months Ended
Jan. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Public Utilities, General Disclosures [Line Items]      
Construction Work in Progress   $ 4,393,900 $ 4,120,700
AEP Texas Inc. [Member]      
Public Utilities, General Disclosures [Line Items]      
Construction Work in Progress   836,200 835,700
Public Service Co Of Oklahoma [Member]      
Public Utilities, General Disclosures [Line Items]      
Construction Work in Progress   94,000 111,300
Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Construction Work in Progress   199,300 $ 233,200
AEP Texas Interim Transmission and Distribution Rates [Member]      
Public Utilities, General Disclosures [Line Items]      
AEP Texas Cumulative Revenues Subject to Review   1,000,000  
Net Increase in Transmission Rates   22,000  
Increase in Transmission Rates Due to Capital Investments   46,000  
Reduction In Transmission Rates Due To Tax Reform   24,000  
Net Decrease In DCRF   24,000  
Increase in Distribution Rates Due to Capital Investments   19,000  
Refund for Current Year Tax Reform Rate Change   21,000  
Refund for Excess ADIT Associated with Certain Depreciable Property   10,000  
Refund for Excess ADIT Not Subject to Rate Normalization Requirements   12,000  
AEP Texas Interim Transmission and Distribution Rates [Member] | AEP Texas Inc. [Member]      
Public Utilities, General Disclosures [Line Items]      
AEP Texas Cumulative Revenues Subject to Review   1,000,000  
Net Increase in Transmission Rates   22,000  
Increase in Transmission Rates Due to Capital Investments   46,000  
Reduction In Transmission Rates Due To Tax Reform   24,000  
Net Decrease In DCRF   24,000  
Increase in Distribution Rates Due to Capital Investments   19,000  
Refund for Current Year Tax Reform Rate Change   21,000  
Refund for Excess ADIT Associated with Certain Depreciable Property   10,000  
Refund for Excess ADIT Not Subject to Rate Normalization Requirements   12,000  
Hurricane Harvey and Texas Storm Cost Securitization [Member]      
Public Utilities, General Disclosures [Line Items]      
Annual Recovery of Storm Costs through Base Rates   1,000  
AEP Texas Total Deferred Storm-Related Costs   152,000  
AEP Texas Hurricane Harvey Deferred Storm-Related Costs   128,600  
AEP Texas Hurricane Harvey Capital Restoration Costs Incurred   219,100  
AEP Texas Hurricane Harvey O&M Restoration Costs Incurred   136,900  
AEP Texas Hurricane Harvey Total Restoration Costs Incurred   356,000  
AEP Texas Hurricane Harvey Incremental O&M Costs   (129,800)  
AEP Texas Hurricane Harvey Incremental Deferred O&M Costs   129,800  
AEP Texas Hurricane Harvey Insurance Proceeds Received Relating to Capital   (12,700)  
AEP Texas Hurricane Harvey Insurance Proceeds Received Relating to Regulatory Assets   (1,200)  
AEP Texas Hurricane Harvey Storm Insurance Proceeds Received   (13,900)  
AEP Texas Hurricane Harvey Storm-Capital Expenditures, Net   206,400  
AEP Texas Hurricane Harvey Total O&M Storm Costs, Net   7,100  
AEP Texas Hurricane Harvey Total Storm Costs, Net   342,100  
Determination of System Restoration Costs for Total Estimated Storm Costs   424,600  
Determination of System Restoration Costs for Total Estimated Storm Costs Net of Offsets   369,600  
Amount of Permanent Storm Restoration Reduction   5,000  
Amount of Disallowed Charges not Directly Related to Storm Restoration   4,000  
Amount of Disallowed Charges due to Additional Insurance Proceeds Received   5,100  
Total Estimated Hurricane Harvey Storm Costs - DSRC   356,000  
Estimated Hurricane Harvey Carrying Costs - DSRC   31,500  
Estimated Litigation Costs - DSRC   600  
Non-Hurricane Harvey Storm Restoration Costs - DSRC   36,500  
Tax Credit - DSRC   (800)  
Insurance Proceeds - DSRC   (8,700)  
Excess ADIT - DSRC [1]   (45,500)  
Settlement Agreement Adjustments - DSRC   (10,600)  
Incremental Insurance Proceeds Received   (5,100)  
Total Estimated Storm Costs Per Settlement Agreement - DSRC   353,900  
Amount of Securitization Request for Distribution Related Assets   247,000  
Amount of Transmission Related Assets to be Recovered at a Later Time   107,000  
Hurricane Harvey and Texas Storm Cost Securitization [Member] | AEP Texas Inc. [Member]      
Public Utilities, General Disclosures [Line Items]      
Annual Recovery of Storm Costs through Base Rates   1,000  
AEP Texas Total Deferred Storm-Related Costs   152,000  
AEP Texas Hurricane Harvey Deferred Storm-Related Costs   128,600  
AEP Texas Hurricane Harvey Capital Restoration Costs Incurred   219,100  
AEP Texas Hurricane Harvey O&M Restoration Costs Incurred   136,900  
AEP Texas Hurricane Harvey Total Restoration Costs Incurred   356,000  
AEP Texas Hurricane Harvey Incremental O&M Costs   (129,800)  
AEP Texas Hurricane Harvey Incremental Deferred O&M Costs   129,800  
AEP Texas Hurricane Harvey Insurance Proceeds Received Relating to Capital   (12,700)  
AEP Texas Hurricane Harvey Insurance Proceeds Received Relating to Regulatory Assets   (1,200)  
AEP Texas Hurricane Harvey Storm Insurance Proceeds Received   (13,900)  
AEP Texas Hurricane Harvey Storm-Capital Expenditures, Net   206,400  
AEP Texas Hurricane Harvey Total O&M Storm Costs, Net   7,100  
AEP Texas Hurricane Harvey Total Storm Costs, Net   342,100  
Determination of System Restoration Costs for Total Estimated Storm Costs   424,600  
Determination of System Restoration Costs for Total Estimated Storm Costs Net of Offsets   369,600  
Amount of Permanent Storm Restoration Reduction   5,000  
Amount of Disallowed Charges not Directly Related to Storm Restoration   4,000  
Amount of Disallowed Charges due to Additional Insurance Proceeds Received   5,100  
Total Estimated Hurricane Harvey Storm Costs - DSRC   356,000  
Estimated Hurricane Harvey Carrying Costs - DSRC   31,500  
Estimated Litigation Costs - DSRC   600  
Non-Hurricane Harvey Storm Restoration Costs - DSRC   36,500  
Tax Credit - DSRC   (800)  
Insurance Proceeds - DSRC   (8,700)  
Excess ADIT - DSRC [1]   (45,500)  
Settlement Agreement Adjustments - DSRC   (10,600)  
Incremental Insurance Proceeds Received   (5,100)  
Total Estimated Storm Costs Per Settlement Agreement - DSRC   353,900  
Amount of Securitization Request for Distribution Related Assets   247,000  
Amount of Transmission Related Assets to be Recovered at a Later Time   107,000  
ETT Interim Transmission Rates [Member]      
Public Utilities, General Disclosures [Line Items]      
Reduction In Transmission Rates Due To Tax Reform   28,000  
Refund for Current Year Tax Reform Rate Change   $ 11,000  
Parent Equity Ownership Interest in ETT   50.00%  
AEP Share of ETT Cumulative Revenues Subject to Review   $ 884,000  
2018 Oklahoma Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   $ 88,000  
Requested Return on Common Equity   10.30%  
Amount Of Increased Depreciation Expense Requested   $ 13,000  
Amount of Increase Related to Increased Storm Expense Amortization   7,000  
2018 Oklahoma Base Rate Case [Member] | Public Service Co Of Oklahoma [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   $ 88,000  
Requested Return on Common Equity   10.30%  
Amount Of Increased Depreciation Expense Requested   $ 13,000  
Amount of Increase Related to Increased Storm Expense Amortization   7,000  
Oklahoma Tax Reform [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   3,000  
Refund for Excess ADIT Associated with Certain Depreciable Property   353,000  
Refund for Excess ADIT Not Subject to Rate Normalization Requirements   72,000  
Oklahoma Tax Reform [Member] | Public Service Co Of Oklahoma [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   3,000  
Refund for Excess ADIT Associated with Certain Depreciable Property   353,000  
Refund for Excess ADIT Not Subject to Rate Normalization Requirements   72,000  
2012 Texas Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
2013 Reversal of Previously Recorded Regulatory Disallowances   114,000  
Resulting Approved Base Rate Increase   $ 52,000  
Texas Jurisdictional Share of Turk Plant   33.00%  
2012 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
2013 Reversal of Previously Recorded Regulatory Disallowances   $ 114,000  
Resulting Approved Base Rate Increase   $ 52,000  
Texas Jurisdictional Share of Turk Plant   33.00%  
2012 Texas Base Rate Case [Member] | Turk Generating Plant [Member]      
Public Utilities, General Disclosures [Line Items]      
Property, Plant and Equipment, Net   $ 1,500,000  
2012 Texas Base Rate Case [Member] | Turk Generating Plant [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Property, Plant and Equipment, Net   $ 1,500,000  
2016 Texas Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Return on Common Equity   10.00%  
Requested Net Increase in Texas Annual Revenues   $ 69,000  
Approved Net Increase in Texas Annual Revenues   50,000  
Approved Additional Vegetation Management Expenses   2,000  
Impairment Charge Total   19,000  
Impairment Charge Welsh Plant, Unit 2   7,000  
Impairment Charge Disallowed Plant Investments   12,000  
Additional Revenues Recognized to be Surcharged to Customers   32,000  
Additional Recognized Expenses Consisting Primarily of Depreciation and Vegetation Management   7,000  
Proposed Revenue Reduction Due to Tax Reform   18,000  
Approved Reduction in Residential Rates Due to Tax Reform   $ 8,000  
Approved Return on Common Equity   9.60%  
2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Return on Common Equity   10.00%  
Requested Net Increase in Texas Annual Revenues   $ 69,000  
Approved Net Increase in Texas Annual Revenues   50,000  
Approved Additional Vegetation Management Expenses   2,000  
Impairment Charge Total   19,000  
Impairment Charge Welsh Plant, Unit 2   7,000  
Impairment Charge Disallowed Plant Investments   12,000  
Additional Revenues Recognized to be Surcharged to Customers   32,000  
Additional Recognized Expenses Consisting Primarily of Depreciation and Vegetation Management   7,000  
Proposed Revenue Reduction Due to Tax Reform   18,000  
Approved Reduction in Residential Rates Due to Tax Reform   $ 8,000  
Approved Return on Common Equity   9.60%  
Texas Tax Reform [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   $ 10,000  
Texas Tax Reform [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   10,000  
2015 Louisiana Formula Rate Filing [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   14,000  
2015 Louisiana Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   14,000  
2017 Louisiana Formula Rate Filing [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   31,000  
Resulting Approved Base Rate Increase   31,000  
2017 Louisiana Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Requested Annual Increase   31,000  
Resulting Approved Base Rate Increase   31,000  
2018 Louisiana Formula Rate Filing [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   11,000  
Requested Annual Increase   28,000  
Adjusted Requested Annual Increase   18,000  
2018 Louisiana Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   11,000  
Requested Annual Increase   28,000  
Adjusted Requested Annual Increase   18,000  
Welsh Plant - Environmental Impact [Member] | Welsh Plant, Units 1 and 3 [Member]      
Public Utilities, General Disclosures [Line Items]      
Property, Plant and Equipment, Net   629,000  
Projected Capital Costs   550,000  
Construction Work in Progress   399,000  
Total Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs   131,000  
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs   79,000  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals   10,000  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity   5,000  
Welsh Plant - Environmental Impact [Member] | Welsh Plant, Units 1 and 3 [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Property, Plant and Equipment, Net   629,000  
Projected Capital Costs   550,000  
Construction Work in Progress   399,000  
Total Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs   131,000  
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs   79,000  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals   10,000  
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity   5,000  
Arkansas Tax Reform [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   7,000  
Refund for Excess ADIT Associated with Certain Depreciable Property   66,000  
Refund for Excess ADIT Not Subject to Rate Normalization Requirements   11,000  
Refund Due to Tax Reform   655  
Arkansas Tax Reform [Member] | Southwestern Electric Power Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Refund for Current Year Tax Reform Rate Change   7,000  
Refund for Excess ADIT Associated with Certain Depreciable Property   66,000  
Refund for Excess ADIT Not Subject to Rate Normalization Requirements   11,000  
Refund Due to Tax Reform   $ 655  
FERC Transmission Complaint - AEP SPP Participants [Member]      
Public Utilities, General Disclosures [Line Items]      
Approved Return on Common Equity   10.70%  
Intervenor Recommended Return on Common Equity   8.36%  
Second Intervenor Recommended Return on Common Equity   8.71%  
FERC SWEPCo Power Supply Agreements Complaint [Member]      
Public Utilities, General Disclosures [Line Items]      
Approved Return on Common Equity   11.10%  
Intervenor Recommended Return on Common Equity   8.41%  
Agreed Upon Return on Common Equity   10.10%  
Agreed Upon One-Time Billing Credit   $ 287  
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member]      
Public Utilities, General Disclosures [Line Items]      
Staff Recommended Annual Increase $ 57,000    
Staff Recommended Return on Common Equity 9.00%    
Oklaunion Power Station Estimated Net Book Value at Retirement $ 49,000    
Intervenor Recommended Refund of SPP Rider 9,000    
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member] | Minimum [Member]      
Public Utilities, General Disclosures [Line Items]      
Intervenor Recommended Annual Increase $ (6,000)    
Intervenor Recommended Return on Common Equity 9.30%    
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member] | Maximum [Member]      
Public Utilities, General Disclosures [Line Items]      
Intervenor Recommended Annual Increase $ 34,000    
Intervenor Recommended Return on Common Equity 9.36%    
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member] | Public Service Co Of Oklahoma [Member]      
Public Utilities, General Disclosures [Line Items]      
Staff Recommended Annual Increase $ 57,000    
Staff Recommended Return on Common Equity 9.00%    
Oklaunion Power Station Estimated Net Book Value at Retirement $ 49,000    
Intervenor Recommended Refund of SPP Rider 9,000    
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member] | Public Service Co Of Oklahoma [Member] | Minimum [Member]      
Public Utilities, General Disclosures [Line Items]      
Intervenor Recommended Annual Increase $ (6,000)    
Intervenor Recommended Return on Common Equity 9.30%    
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member] | Public Service Co Of Oklahoma [Member] | Maximum [Member]      
Public Utilities, General Disclosures [Line Items]      
Intervenor Recommended Annual Increase $ 34,000    
Intervenor Recommended Return on Common Equity 9.36%    
[1] (a)Amount represents Non-Hurricane Harvey Excess ADIT that is not subject to rate normalization requirements.