BENEFIT PLANS - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 25	$ 24
Interest Cost	51	53
Expected Return on Plan Assets	(64)	(70)
Amortization of Net Actuarial Gain (Loss)	11	4
Net Periodic Benefit Cost	23	11
Pension Plans | AEP Texas
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	2
Interest Cost	4	5
Expected Return on Plan Assets	(5)	(6)
Amortization of Net Actuarial Gain (Loss)	1	0
Net Periodic Benefit Cost	2	1
Pension Plans | APCo
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	2
Interest Cost	6	6
Expected Return on Plan Assets	(8)	(9)
Amortization of Net Actuarial Gain (Loss)	1	1
Net Periodic Benefit Cost	1	0
Pension Plans | I&M
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3	3
Interest Cost	6	6
Expected Return on Plan Assets	(8)	(9)
Amortization of Net Actuarial Gain (Loss)	1	0
Net Periodic Benefit Cost	2	0
Pension Plans | OPCo
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	2
Interest Cost	5	5
Expected Return on Plan Assets	(7)	(7)
Amortization of Net Actuarial Gain (Loss)	1	0
Net Periodic Benefit Cost	1	0
Pension Plans | PSO
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	1
Interest Cost	3	3
Expected Return on Plan Assets	(4)	(4)
Amortization of Net Actuarial Gain (Loss)	0	0
Net Periodic Benefit Cost	1	0
Pension Plans | SWEPCo
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	2
Interest Cost	3	3
Expected Return on Plan Assets	(4)	(4)
Amortization of Net Actuarial Gain (Loss)	1	0
Net Periodic Benefit Cost	2	1
OPEB
Defined Benefit Plan Disclosure [Line Items]
Service Cost	1	1
Interest Cost	8	8
Expected Return on Plan Assets	(29)	(28)
Amortization of Prior Service Credit	(1)	(1)
Amortization of Net Actuarial Gain (Loss)	(1)
Net Periodic Benefit Cost	(22)	(20)
OPEB | AEP Texas
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	1	1
Expected Return on Plan Assets	(3)	(3)
Amortization of Prior Service Credit	0	0
Amortization of Net Actuarial Gain (Loss)	0
Net Periodic Benefit Cost	(2)	(2)
OPEB | APCo
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	1	1
Expected Return on Plan Assets	(4)	(4)
Amortization of Prior Service Credit	0	0
Amortization of Net Actuarial Gain (Loss)	0
Net Periodic Benefit Cost	(3)	(3)
OPEB | I&M
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	1	1
Expected Return on Plan Assets	(4)	(3)
Amortization of Prior Service Credit	0	0
Amortization of Net Actuarial Gain (Loss)	0
Net Periodic Benefit Cost	(3)	(2)
OPEB | OPCo
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	1	1
Expected Return on Plan Assets	(3)	(3)
Amortization of Prior Service Credit	0	0
Amortization of Net Actuarial Gain (Loss)	0
Net Periodic Benefit Cost	(2)	(2)
OPEB | PSO
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	0	0
Expected Return on Plan Assets	(1)	(1)
Amortization of Prior Service Credit	0	0
Amortization of Net Actuarial Gain (Loss)	0
Net Periodic Benefit Cost	(1)	(1)
OPEB | SWEPCo
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	1	1
Expected Return on Plan Assets	(2)	(2)
Amortization of Prior Service Credit	0	0
Amortization of Net Actuarial Gain (Loss)	0
Net Periodic Benefit Cost	$ (1)	$ (1)