Rate Matters West Companies (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) customer	Dec. 31, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress	$ 4,289.5	$ 4,025.7
AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress	567.8	614.1
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress	98.2	128.7
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress	232.4	$ 228.3
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	$ 118.0
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	$ 1,200.0
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
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
Hurricane Laura [Member] | Southwestern Electric Power Co [Member] | Louisiana Jurisdiction [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Other Operation and Maintenance Expenses	$ 79.0
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	$ 82.0
Capitalized Storm Costs	$ 31.0
Hurricane Delta [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Customers without Power | customer	23,000
Incremental Other Operation and Maintenance Expenses	$ 17.0
Capitalized Storm Costs	3.0
2020 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase	105.0
Staff Recommended Annual Rate Increase	$ 45.0
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
Staff Recommended Return on Common Equity	9.22%
2020 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Recommended Annual Increase	$ 20.0
Intervenor Recommended Return on Common Equity	9.00%
2020 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Recommended Annual Increase	$ 70.0
Intervenor Recommended Return on Common Equity	9.15%
2020 Louisiana Base Rate Case | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase	$ 134.0
Requested Return on Equity	10.35%
Amount of Increase Related to Annual Depreciation Expense	$ 32.0
Amount of Increase Related to Recovering Deferred Hurricane Costs	$ 10.0