Rate Matters - West Companies (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress	$ 3,336.8	$ 3,183.9
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress	111.2	148.2
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress	116.1	$ 113.8
AEP Texas Interim Transmission and Distribution Rates [Member]
Public Utilities, General Disclosures [Line Items]
AEP Texas Cumulative Revenues Subject to Review	$ 635.0
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	$ 672.0
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	8.36%
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 Return on Common Equity	10.00%
Requested Net Increase in Texas Annual Revenues	$ 69.0
Amount Of Increase Related To Environmental Controls	34.0
Amount of Increase Related to Additonal Investment and Increased Operating Costs	25.0
Amount of Increase Related to Transmission Cost Recovery	8.0
Amount of Increase Related to Vegetation Management	$ 2.0
Texas Jurisdictional Share of the Welsh Plant	33.00%
Recommended Investment Disallowances Resulting in Possible Write-Offs	$ 89.0
Amount of Write-Off Related to Environmental Controls	40.0
Amount of Write-Off Related to Welsh Plant Unit 2	$ 25.0
2016 Texas Base Rate Case [Member] \| Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Return on Common Equity	10.00%
Requested Net Increase in Texas Annual Revenues	$ 69.0
Amount Of Increase Related To Environmental Controls	34.0
Amount of Increase Related to Additonal Investment and Increased Operating Costs	25.0
Amount of Increase Related to Transmission Cost Recovery	8.0
Amount of Increase Related to Vegetation Management	$ 2.0
Texas Jurisdictional Share of the Welsh Plant	33.00%
Recommended Investment Disallowances Resulting in Possible Write-Offs	$ 89.0
Amount of Write-Off Related to Environmental Controls	40.0
Amount of Write-Off Related to Welsh Plant Unit 2	$ 25.0
Louisiana Turk Plant Prudence Review [Member]
Public Utilities, General Disclosures [Line Items]
Louisiana Jurisdictional Share Of Turk Plant	29.00%
Louisiana Turk Plant Prudence Review [Member] \| Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Louisiana Jurisdictional Share Of Turk Plant	29.00%
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
Oklahoma Base Rate Case - 2017 [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase	$ 156.0
Requested Return on Common Equity	10.00%
Amount of Increase Related to Annual Depreciation Rates	$ 42.0
Oklahoma Base Rate Case - 2017 [Member] \| Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase	$ 156.0
Requested Return on Common Equity	10.00%
Amount of Increase Related to Annual Depreciation Rates	$ 42.0
Oklahoma Base Rate Case - 2017 [Member] \| Northeastern Plant, Unit 4 [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net	83.0
Oklahoma Base Rate Case - 2017 [Member] \| Northeastern Plant, Unit 4 [Member] \| Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net	83.0
Welsh Plant, Units 1 and 3 - Environmental Projects [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs	850.0
Construction Work in Progress	398.0
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs	79.0
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
Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs	131.0
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	398.0
Total Amount of Recovery Requested Related to Arkansas Retail Jurisdictional Share of Environmental Costs	79.0
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
Amount Of Recovery Requested Related To Louisiana Retail Jurisdictional Share Of Environmental Costs	131.0
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	628.0
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	628.0
Minimum [Member] \| 2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Texas Annual Revenues	$ 36.0
Recommended Return on Equity	9.20%
Minimum [Member] \| 2016 Texas Base Rate Case [Member] \| Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Texas Annual Revenues	$ 36.0
Recommended Return on Equity	9.20%
Maximum [Member] \| 2016 Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Texas Annual Revenues	$ 47.0
Recommended Return on Equity	9.35%
Maximum [Member] \| 2016 Texas Base Rate Case [Member] \| Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Recommended Net Increase in Texas Annual Revenues	$ 47.0
Recommended Return on Equity	9.35%

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