Rate Matters - West Companies (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Jul. 26, 2018	Jun. 30, 2018	Dec. 31, 2017
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 4,630,300	$ 4,120,700
AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		1,009,100	835,700
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		103,100	111,300
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		228,600	$ 233,200
AEP Texas Interim Transmission and Distribution Rates [Member]
Public Utilities, General Disclosures [Line Items]
AEP Texas Cumulative Revenues Subject to Review		894,000
Reduction in Transmission Rates Due to Tax Reform		24,000
Net Decrease In DCRF		5,000
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		894,000
Reduction in Transmission Rates Due to Tax Reform		24,000
Net Decrease In DCRF		5,000
Hurricane Harvey Storm [Member]
Public Utilities, General Disclosures [Line Items]
Annual Recovery of Storm Costs through Base Rates		1,000
AEP Texas Total Storm-Related Costs		145,000
AEP Texas Hurricane Harvey Storm-Related Costs		121,000
AEP Texas Hurricane Harvey Storm-Capital Expenditures		199,000
Hurricane Harvey Storm Insurance Proceeds Received		10,000
Hurricane Harvey Storm [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Annual Recovery of Storm Costs through Base Rates		1,000
AEP Texas Total Storm-Related Costs		145,000
AEP Texas Hurricane Harvey Storm-Related Costs		121,000
AEP Texas Hurricane Harvey Storm-Capital Expenditures		199,000
Hurricane Harvey Storm Insurance Proceeds Received		10,000
ETT Interim Transmission Rates [Member]
Public Utilities, General Disclosures [Line Items]
Reduction in Transmission Rates Due to Tax Reform		$ 28,000
Parent Ownership Interest In ETT		50.00%
AEP Share Of ETT Cumulative Revenues Subject To Review		$ 815,000
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%
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
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
2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Requested Net Increase in Texas Annual Revenues		$ 69,000
Requested Return on Common Equity		10.00%
Approved Net Increase in Texas Annual Revenues		$ 50,000
Approved Return on Common Equity		9.60%
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
2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Net Increase in Texas Annual Revenues		$ 69,000
Requested Return on Common Equity		10.00%
Approved Net Increase in Texas Annual Revenues		$ 50,000
Approved Return on Common Equity		9.60%
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
Louisiana 2015 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		14,000
Louisiana 2015 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		14,000
Louisiana 2017 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		31,000
Louisiana 2017 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		31,000
Louisiana 2018 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		28,000
Louisiana 2018 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		28,000
Welsh Plant, Units 1 and 3 - Environmental Projects [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		550,000
Construction Work in Progress		399,000
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs		79,000
Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs		131,000
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals		11,000
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		6,000
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		550,000
Construction Work in Progress		399,000
Property, Plant and Equipment, Net		624,000
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs		79,000
Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs		131,000
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals		11,000
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		6,000
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		$ 624,000
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] | Louisiana 2018 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Adjusted Requested Annual Increase	$ 18,000
Subsequent Event [Member] | Louisiana 2018 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Adjusted Requested Annual Increase	$ 18,000