REVENUE FROM CONTRACTS WITH CUSTOMERS - Affiliate Accounts Receivable (Details) - Related Party - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
AEP Texas
Disaggregation of Revenue [Line Items]
Affiliated Companies	$ 0.1	$ 0.0
AEPTCo
Disaggregation of Revenue [Line Items]
Affiliated Companies	143.7	131.6
APCo
Disaggregation of Revenue [Line Items]
Affiliated Companies	93.9	83.7
I&M
Disaggregation of Revenue [Line Items]
Affiliated Companies	58.2	55.0
OPCo
Disaggregation of Revenue [Line Items]
Affiliated Companies	65.3	63.6
PSO
Disaggregation of Revenue [Line Items]
Affiliated Companies	19.9	13.0
SWEPCo
Disaggregation of Revenue [Line Items]
Affiliated Companies	$ 53.0	$ 21.4