REVENUE FROM CONTRACTS WITH CUSTOMERS - Affiliate Accounts Receivable (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
AEP TEXAS INC.
Disaggregation of Revenue [Line Items]
Affiliated Companies	$ 15	$ 11
AEP TRANSMISSION COMPANY, LLC
Disaggregation of Revenue [Line Items]
Affiliated Companies	153	134
APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	142	110
INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	90	79
OHIO POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	132	118
PUBLIC SERVICE COMPANY OF OKLAHOMA
Disaggregation of Revenue [Line Items]
Affiliated Companies	45	33
SOUTHWESTERN ELECTRIC POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	91	54
Related Party | AEP TRANSMISSION COMPANY, LLC
Disaggregation of Revenue [Line Items]
Affiliated Companies	146	132
Related Party | APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	113	84
Related Party | INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	67	55
Related Party | OHIO POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	74	64
Related Party | PUBLIC SERVICE COMPANY OF OKLAHOMA
Disaggregation of Revenue [Line Items]
Affiliated Companies	22	13
Related Party | SOUTHWESTERN ELECTRIC POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	$ 65	$ 21