Rate Matters West Companies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 4,759.4	$ 4,120.7
AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		951.6	835.7
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		110.3	111.3
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		266.9	$ 233.2
AEP Texas Interim Transmission and Distribution Rates [Member]
Public Utilities, General Disclosures [Line Items]
AEP Texas Cumulative Revenues Subject to Review		830.0
Proposed Reduction in Transmission Rates Due to Tax Reform		24.0
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		830.0
Proposed Reduction in Transmission Rates Due to Tax Reform		24.0
Hurricane Harvey Storm [Member]
Public Utilities, General Disclosures [Line Items]
Annual Recovery of Storm Costs through Base Rates		1.0
AEP Texas Total Storm-Related Costs		129.0
AEP Texas Hurricane Harvey Storm-Related Costs		105.0
AEP Texas Hurricane Harvey Storm-Capital Expenditures		186.0
Hurricane Harvey Storm Insurance Proceeds Received		10.0
Hurricane Harvey Storm [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		129.0
AEP Texas Hurricane Harvey Storm-Related Costs		105.0
AEP Texas Hurricane Harvey Storm-Capital Expenditures		186.0
Hurricane Harvey Storm Insurance Proceeds Received		10.0
ETT Interim Transmission Rates [Member]
Public Utilities, General Disclosures [Line Items]
Proposed Reduction in Transmission Rates Due to Tax Reform		$ 27.0
Parent Ownership Interest In ETT		50.00%
AEP Share Of ETT Cumulative Revenues Subject To Review		$ 781.0
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
2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Requested Net Increase in Texas Annual Revenues		$ 69.0
Requested Return on Equity		10.00%
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
2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Net Increase in Texas Annual Revenues		$ 69.0
Requested Return on Equity		10.00%
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 2015 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		14.0
Louisiana 2015 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		14.0
Louisiana 2017 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		31.0
Louisiana 2017 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		31.0
Welsh Plant, Units 1 and 3 - Environmental Projects [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		850.0
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		11.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		6.0
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		850.0
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		11.0
Amount of LPSC Approved Eligible Welsh Plant Environmental Control Deferred Unrecognized Equity		6.0
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		625.0
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		$ 625.0
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%
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 Range		8.41%
Subsequent Event [Member] | AEP Texas Interim Transmission and Distribution Rates [Member]
Public Utilities, General Disclosures [Line Items]
Proposed Net Increase in DCRF	$ 3.0
Proposed Increase in DCRF Due to Capital Investments	24.0
Proposed Reduction in DCRF Due to Tax Reform	21.0
Subsequent Event [Member] | AEP Texas Interim Transmission and Distribution Rates [Member] | AEP Texas Inc. [Member]
Public Utilities, General Disclosures [Line Items]
Proposed Net Increase in DCRF	3.0
Proposed Increase in DCRF Due to Capital Investments	24.0
Proposed Reduction in DCRF Due to Tax Reform	21.0
Subsequent Event [Member] | 2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Proposed Revenue Reduction Due to Tax Reform	18.0
Subsequent Event [Member] | 2016 Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Proposed Revenue Reduction Due to Tax Reform	18.0
Subsequent Event [Member] | Louisiana 2018 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase	28.0
Subsequent Event [Member] | Louisiana 2018 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase	$ 28.0