Rate Matters West Companies (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 22, 2020 USD ($) customer	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) customer	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 4,662.5		$ 4,662.5		$ 4,319.8
AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		787.9		787.9		763.9
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		147.2		147.2		133.4
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Provision for Refund		2.4	$ (0.1)	(2.0)	$ (25.3)
Construction Work in Progress		272.3		272.3		$ 216.9
2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase				$ 56.0
Requested Return on Equity				10.50%
Refund for Excess ADIT				$ 21.0
Approved Annual Revenue Decrease				40.0
Other Asset Impairment Charges				33.0
Refund for Excess ADIT Associated with Certain Depreciable Property				$ 275.0
Approved Return on Common Equity				9.40%
Public Utilities, Approved Debt Capital Structure, Percentage				57.50%
Public Utilities, Approved Equity Capital Structure, Percentage				42.50%
2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member] | Capital Investments [Member]
Public Utilities, General Disclosures [Line Items]
Disallowed Item in Commission Order				$ 23.0
2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member] | Rate Case Expense [Member]
Public Utilities, General Disclosures [Line Items]
Write-off of Regulatory Expense				4.0
Disallowed Item in Commission Order				4.0
2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member] | Amount of 2019 Investments [Member]
Public Utilities, General Disclosures [Line Items]
Other Asset Impairment Charges				10.0
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				$ 38.0
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				$ 1,100.0
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
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		$ 1,400.0		$ 1,400.0
Texas Jurisdictional Share of Turk Plant				33.00%
2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Return on Equity				10.00%
Requested Net Increase in Texas Annual Revenues				$ 69.0
Approved Net Increase in Texas Annual Revenues				$ 50.0
Approved Return on Common Equity				9.60%
Approved Additional Vegetation Management Expenses				$ 2.0
Impairment Charge Total				19.0
Impairment Charge Welsh Plant, Unit 2				7.0
Impairment Charge Disallowed Plant Investments				12.0
Additional Revenues Recognized to be Surcharged to Customers				32.0
Additional Recognized Expenses Consisting Primarily of Depreciation and Vegetation Management				7.0
Louisiana 2018 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase				28.0
Adjusted Requested Annual Increase				18.0
Refund for Current Year Tax Reform Rate Change				11.0
Additional Refund for Current Year Tax Reform Rate Change				4.0
Staff Recommended Annual Rate Increase				14.0
Refund for Over Collections				6.0
Hurricane Laura [Member] | Southwestern Electric Power Co [Member] | Louisiana Jurisdiction [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Other Operation and Maintenance Expenses				67.0
Capitalized Storm Costs				$ 30.0
Hurricane Laura [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Customers without Power | customer				130,000
Incremental Other Operation and Maintenance Expenses				$ 69.0
Capitalized Storm Costs				31.0
Subsequent Event [Member] | Hurricane Delta [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Customers without Power | customer	23,000
Subsequent Event [Member] | Hurricane Delta [Member] | Southwestern Electric Power Co [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Other Operation and Maintenance Expenses	$ 10.0
Subsequent Event [Member] | Hurricane Delta [Member] | Southwestern Electric Power Co [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Other Operation and Maintenance Expenses	18.0
Capitalized Storm Costs	6.0
Subsequent Event [Member] | 2020 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase	$ 105.0
Requested Return on Equity	10.35%
Requested Net Annual Increase	$ 90.0
Amount of Increase Related to Vegetation Management	5.0
Amount of Increase Related to Annual Depreciation Expense	10.0
Amount of Increase Related to Storm Catastrophe Reserve	2.0
Requested Recovery of Dolet Hills Power Station	$ 45.0
Capitalized Vegetation Management Expenses [Member] | 2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Approved Item in Commission Order				26.0
Excess ADIT and Excess Federal Income Taxes to Distribution Customers [Member] | 2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Item to be Refunded in Commission Order				77.0
Excess ADIT and Excess Federal Income Taxes to Transmission Customers [Member] | 2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Item to be Refunded in Commission Order				31.0
Previously Collected Rates Subject to Reconciliation [Member] | 2019 Texas Base Rate Case [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Item to be Refunded in Commission Order				30.0
Provision for Refund				$ 30.0