REVENUE FROM CONTRACTS WITH CUSTOMERS - Affiliate Accounts Receivable (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
AEP TEXAS INC.
Disaggregation of Revenue [Line Items]
Affiliated Companies	$ 19	$ 15
AEP TRANSMISSION COMPANY, LLC
Disaggregation of Revenue [Line Items]
Affiliated Companies	178	153
APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	236	142
INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	141	90
OHIO POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	194	132
PUBLIC SERVICE COMPANY OF OKLAHOMA
Disaggregation of Revenue [Line Items]
Affiliated Companies	84	45
SOUTHWESTERN ELECTRIC POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	133	91
Related Party | AEP TEXAS INC.
Disaggregation of Revenue [Line Items]
Affiliated Companies	2	0
Related Party | AEP TRANSMISSION COMPANY, LLC
Disaggregation of Revenue [Line Items]
Affiliated Companies	165	146
Related Party | APPALACHIAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	198	113
Related Party | INDIANA MICHIGAN POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	119	67
Related Party | OHIO POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	133	74
Related Party | PUBLIC SERVICE COMPANY OF OKLAHOMA
Disaggregation of Revenue [Line Items]
Affiliated Companies	57	22
Related Party | SOUTHWESTERN ELECTRIC POWER COMPANY
Disaggregation of Revenue [Line Items]
Affiliated Companies	$ 85	$ 65