FAIR VALUE MEASUREMENTS - Debt Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	$ 46,137.6	$ 42,642.8
Fair Value	43,486.2	38,964.7
AEP Texas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	7,264.5	6,441.6
Fair Value	6,884.4	5,831.4
AEPTCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	6,240.4	5,768.1
Fair Value	5,515.5	4,853.1
APCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	5,758.1	5,660.3
Fair Value	5,647.6	5,346.0
I&M
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,485.1	3,494.3
Fair Value	3,250.1	3,153.8
OPCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,717.8	3,715.7
Fair Value	3,356.7	3,203.4
PSO
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,524.6	2,855.6
Fair Value	3,365.0	2,562.1
SWEPCo
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Book Value	3,972.6	3,980.8
Fair Value	$ 3,626.6	$ 3,431.5