FINANCING ACTIVITIES - Financing Activities Subsequent Events (Details) - USD ($) $ in Millions		1 Months Ended		3 Months Ended
	May 05, 2026	Apr. 30, 2026	Mar. 31, 2026	Mar. 31, 2026	Mar. 31, 2025
Debt Instrument [Line Items]
Total Issuances				$ 2,932
Repayments of long-term debt				678	$ 229
PUBLIC SERVICE COMPANY OF OKLAHOMA
Debt Instrument [Line Items]
Repayments of long-term debt				$ 0	125
SOUTHWESTERN ELECTRIC POWER COMPANY | Notes Payable
Debt Instrument [Line Items]
Interest rate (in percentage)			4.24%	4.24%
Repayments of long-term debt			$ 1,000
INDIANA MICHIGAN POWER COMPANY
Debt Instrument [Line Items]
Repayments of long-term debt				$ 31	27
AEP TRANSMISSION COMPANY, LLC
Debt Instrument [Line Items]
Repayments of long-term debt				101	$ 50
AEP TRANSMISSION COMPANY, LLC | Other Long-term Debt
Debt Instrument [Line Items]
Total Issuances				$ 114
Subsequent Event | Pollution Control Bonds
Debt Instrument [Line Items]
Total Issuances		$ 50
Interest rate (in percentage)		3.50%
Repayments of long-term debt	$ 50
Subsequent Event | OHIO POWER COMPANY
Debt Instrument [Line Items]
Proceeds from contributed capital		$ 64
Subsequent Event | PUBLIC SERVICE COMPANY OF OKLAHOMA
Debt Instrument [Line Items]
Proceeds from contributed capital		113
Subsequent Event | SOUTHWESTERN ELECTRIC POWER COMPANY
Debt Instrument [Line Items]
Proceeds from contributed capital		81
Subsequent Event | INDIANA MICHIGAN POWER COMPANY | Notes Payable
Debt Instrument [Line Items]
Repayments of long-term debt		11
Subsequent Event | AEP TRANSMISSION COMPANY, LLC | Other Long-term Debt
Debt Instrument [Line Items]
Repayments of long-term debt		$ 62