Rate Matters West Companies (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 4,910.9	$ 4,393.9
AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		941.8	836.2
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		98.6	94.0
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		193.4	$ 199.3
AEP Texas Interim Transmission and Distribution Rates [Member]
Public Utilities, General Disclosures [Line Items]
AEP Texas Cumulative Revenues Subject to Review		1,100.0
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		1,100.0
Texas Storm Cost Securitization [Member]
Public Utilities, General Disclosures [Line Items]
Annual Recovery of Storm Costs through Base Rates		1.0
AEP Texas Total Storm-Related Costs		152.0
AEP Texas Hurricane Harvey Storm-Related Costs		137.0
Distribution-Related System Restoration Costs		264.6
Estimated Carrying Costs		26.9
Up-front Qualified Costs		4.6
Total Distribution-Related System Restoration Costs		296.1
Insurance Proceeds and Government Grants		(3.1)
Excess ADIT	[1]	(63.5)
Securitization Request for Distribution Related Assets		229.5
Transmission Related Assets to be Recovered at a Later Time		95.0
Texas Storm Cost Securitization [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Annual Recovery of Storm Costs through Base Rates		1.0
AEP Texas Total Storm-Related Costs		152.0
AEP Texas Hurricane Harvey Storm-Related Costs		137.0
Distribution-Related System Restoration Costs		264.6
Estimated Carrying Costs		26.9
Up-front Qualified Costs		4.6
Total Distribution-Related System Restoration Costs		296.1
Insurance Proceeds and Government Grants		(3.1)
Excess ADIT	[1]	(63.5)
Securitization Request for Distribution Related Assets		229.5
Transmission Related Assets to be Recovered at a Later Time		$ 95.0
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		$ 918.0
2018 Oklahoma Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 88.0
Requested Return on Equity		10.30%
Amount Of Increased Depreciation Expense Requested		$ 13.0
Amount of Increase Related to Increased Storm Expense Amortization		7.0
Approved Annual Revenue Increase		$ 46.0
Approved Return on Common Equity		9.40%
Revenue Cap on New Distribution Reliability and Safety Rider		$ 5.0
2018 Oklahoma Base Rate Case [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 88.0
Requested Return on Equity		10.30%
Amount Of Increased Depreciation Expense Requested		$ 13.0
Amount of Increase Related to Increased Storm Expense Amortization		7.0
Approved Annual Revenue Increase		$ 46.0
Approved Return on Common Equity		9.40%
Revenue Cap on New Distribution Reliability and Safety Rider		$ 5.0
2012 Texas Base Rate Case [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] | 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]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		$ 1,500.0
Texas Jurisdictional Share of Turk Plant		33.00%
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		$ 1,500.0
Texas Jurisdictional Share of Turk Plant		33.00%
2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Requested Return on Equity		10.00%
Approved Return on Common Equity		9.60%
Requested Net Increase in Texas Annual Revenues		$ 69.0
Approved Net Increase in Texas Annual Revenues		50.0
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
2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Return on Equity		10.00%
Approved Return on Common Equity		9.60%
Requested Net Increase in Texas Annual Revenues		$ 69.0
Approved Net Increase in Texas Annual Revenues		50.0
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]
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
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
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		623.0
Projected Capital Costs		550.0
Construction Work in Progress		399.0
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs		79.0
Total Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs		131.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals		10.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		5.0
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		623.0
Projected Capital Costs		550.0
Construction Work in Progress		399.0
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs		79.0
Total Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs		131.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferrals		10.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		5.0
2019 Arkansas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 75.0
Requested Return on Equity		10.50%
Requested Annual Net Increase		$ 58.0
Requested Additional Vegetation Management Expenses		12.0
2019 Arkansas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 75.0
Requested Return on Equity		10.50%
Requested Annual Net Increase		$ 58.0
Requested Additional Vegetation Management Expenses		$ 12.0
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 Range		8.36%
Second Intervenor Recommended Return on Common Equity		8.71%
Return On Common Equity Per Settlement Agreement		10.00%
Return on Common Equity Inclusive of RTO Per Settlement Agreement		10.50%
RTO Incentive Adder Per Settlement Agreement		0.50%

[1] (a)Amount represents Non-Hurricane Harvey Excess ADIT that is not subject to rate normalization requirements.