Rate Matters - West Companies (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Oct. 25, 2018	Sep. 30, 2018	Dec. 31, 2017
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 4,995,500	$ 4,120,700
AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		1,108,800	835,700
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		85,700	111,300
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		234,500	$ 233,200
AEP Texas Interim Transmission and Distribution Rates [Member]
Public Utilities, General Disclosures [Line Items]
AEP Texas Cumulative Revenues Subject to Review		959,000
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		959,000
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 Storm [Member]
Public Utilities, General Disclosures [Line Items]
Annual Recovery of Storm Costs through Base Rates		1,000
AEP Texas Total Storm-Related Costs		150,000
AEP Texas Hurricane Harvey Storm-Related Costs		127,000
AEP Texas Hurricane Harvey Storm-Capital Expenditures		205,000
Hurricane Harvey Storm Insurance Proceeds Received		10,000
AEP Texas Hurricane Harvey Storm-Insurance Proceeds to be Received		4,000
Determination of System Restoration Costs for Total Estimated Storm Costs		425,000
Determination of System Restoration Costs for Total Estimated Storm Costs Net of Offsets		370,000
Amount of Securitization Request for Distribution Related Assets		253,000
Amount of Transmission Related Assets to be Recovered at a Later Time		117,000
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		150,000
AEP Texas Hurricane Harvey Storm-Related Costs		127,000
AEP Texas Hurricane Harvey Storm-Capital Expenditures		205,000
Hurricane Harvey Storm Insurance Proceeds Received		10,000
AEP Texas Hurricane Harvey Storm-Insurance Proceeds to be Received		4,000
Determination of System Restoration Costs for Total Estimated Storm Costs		425,000
Determination of System Restoration Costs for Total Estimated Storm Costs Net of Offsets		370,000
Amount of Securitization Request for Distribution Related Assets		253,000
Amount of Transmission Related Assets to be Recovered at a Later Time		117,000
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 Ownership Interest In ETT		50.00%
AEP Share Of ETT Cumulative Revenues Subject To Review		$ 849,000
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
FERC Transmission Complaint - AEP SPP Participants [Member]
Public Utilities, General Disclosures [Line Items]
Approved Return on Common Equity		10.70%
Second Intervenor Recommended Return on Common Equity		8.71%
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
Adjusted Requested Annual Increase		18,000
Louisiana 2018 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		28,000
Adjusted Requested Annual Increase		18,000
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		10,000
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
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		10,000
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		621,000
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		621,000
Arkansas Tax Reform [Member]
Public Utilities, General Disclosures [Line Items]
Refund Due to Tax Reform		655
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
Arkansas Tax Reform [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Refund Due to Tax Reform		655
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
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] | Hurricane Harvey Storm [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Requested Reduction in Amount of Securitization for Distribution Related Assets	$ 24,000
PUCT Staff Requested Reduction in Amount of Securitization for Distribution Related Assets	4,000
Subsequent Event [Member] | Hurricane Harvey Storm [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Requested Reduction in Amount of Securitization for Distribution Related Assets	24,000
PUCT Staff Requested Reduction in Amount of Securitization for Distribution Related Assets	4,000
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Net Increase	88,000
Amount of Increase Related to Increased Storm Expense Amortization	$ 7,000
Requested Return on Common Equity	10.30%
Amount of Increase Related to Annual Depreciation Rates	$ 13,000
Subsequent Event [Member] | 2018 Oklahoma Base Rate Case [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Net Increase	88,000
Amount of Increase Related to Increased Storm Expense Amortization	$ 7,000
Requested Return on Common Equity	10.30%
Amount of Increase Related to Annual Depreciation Rates	$ 13,000
Subsequent Event [Member] | Texas Tax Reform [Member]
Public Utilities, General Disclosures [Line Items]
Refund for Current Year Tax Reform Rate Change	10,000
Subsequent Event [Member] | 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
Subsequent Event [Member] | Louisiana 2017 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Resulting Approved Base Rate Increase	31,000
Subsequent Event [Member] | Louisiana 2017 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Resulting Approved Base Rate Increase	31,000
Subsequent Event [Member] | Louisiana 2018 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Refund for Current Year Tax Reform Rate Change	11,000
Subsequent Event [Member] | Louisiana 2018 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