v3.25.2
BENEFIT PLANS - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Pension Plans        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost $ 23.9 $ 25.6 $ 47.9 $ 51.2
Interest Cost 52.8 51.9 105.6 103.8
Expected Return on Plan Assets (70.2) (80.2) (140.5) (160.4)
Amortization of Net Actuarial Gain (Loss) 4.0 1.1 8.1 2.2
Net Periodic Benefit Cost (Credit) 10.5 (1.6) 21.1 (3.2)
Pension Plans | AEP Texas        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 2.2 2.2 4.4 4.4
Interest Cost 4.3 4.4 8.8 8.7
Expected Return on Plan Assets (5.5) (6.6) (11.1) (13.0)
Amortization of Net Actuarial Gain (Loss) 0.4 0.1 0.7 0.2
Net Periodic Benefit Cost (Credit) 1.4 0.1 2.8 0.3
Pension Plans | APCo        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 2.2 2.5 4.6 4.9
Interest Cost 6.3 6.2 12.5 12.4
Expected Return on Plan Assets (9.4) (10.7) (18.8) (21.4)
Amortization of Net Actuarial Gain (Loss) 0.5 0.1 0.9 0.2
Net Periodic Benefit Cost (Credit) (0.4) (1.9) (0.8) (3.9)
Pension Plans | I&M        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 3.1 3.3 6.3 6.6
Interest Cost 6.2 5.9 12.4 11.9
Expected Return on Plan Assets (9.7) (10.6) (19.4) (21.4)
Amortization of Net Actuarial Gain (Loss) 0.5 0.1 0.9 0.2
Net Periodic Benefit Cost (Credit) 0.1 (1.3) 0.2 (2.7)
Pension Plans | OPCo        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 2.3 2.3 4.6 4.7
Interest Cost 4.8 4.7 9.7 9.4
Expected Return on Plan Assets (7.4) (8.1) (14.7) (16.3)
Amortization of Net Actuarial Gain (Loss) 0.4 0.0 0.7 0.1
Net Periodic Benefit Cost (Credit) 0.1 (1.1) 0.3 (2.1)
Pension Plans | PSO        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 1.6 1.6 3.0 3.1
Interest Cost 2.5 2.5 5.2 5.0
Expected Return on Plan Assets (3.8) (4.4) (7.7) (8.7)
Amortization of Net Actuarial Gain (Loss) 0.1 0.1 0.3 0.1
Net Periodic Benefit Cost (Credit) 0.4 (0.2) 0.8 (0.5)
Pension Plans | SWEPCo        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 1.9 2.1 3.8 4.0
Interest Cost 3.0 3.1 6.2 6.2
Expected Return on Plan Assets (3.6) (4.4) (7.3) (8.8)
Amortization of Net Actuarial Gain (Loss) 0.3 0.0 0.5 0.1
Net Periodic Benefit Cost (Credit) 1.6 0.8 3.2 1.5
OPEB        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 1.0 1.1 1.8 2.2
Interest Cost 8.6 10.6 17.2 21.1
Expected Return on Plan Assets (28.3) (27.9) (56.5) (55.7)
Amortization of Prior Service Credit (0.6) (3.2) (1.2) (6.4)
Amortization of Net Actuarial Gain (Loss) (0.3) 0.7 (0.6) 1.5
Net Periodic Benefit Cost (Credit) (19.6) (18.7) (39.3) (37.3)
OPEB | AEP Texas        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 0.1 0.1 0.2 0.2
Interest Cost 0.7 0.8 1.3 1.6
Expected Return on Plan Assets (2.4) (2.2) (4.7) (4.5)
Amortization of Prior Service Credit (0.1) (0.2) (0.1) (0.5)
Amortization of Net Actuarial Gain (Loss) 0.0 0.0 0.0 0.1
Net Periodic Benefit Cost (Credit) (1.7) (1.5) (3.3) (3.1)
OPEB | APCo        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 0.2 0.1 0.3 0.2
Interest Cost 1.3 1.6 2.7 3.3
Expected Return on Plan Assets (4.1) (4.1) (8.2) (8.1)
Amortization of Prior Service Credit (0.1) (0.4) (0.2) (0.9)
Amortization of Net Actuarial Gain (Loss) (0.1) 0.1 (0.2) 0.2
Net Periodic Benefit Cost (Credit) (2.8) (2.7) (5.6) (5.3)
OPEB | I&M        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 0.2 0.2 0.3 0.3
Interest Cost 0.9 1.2 1.9 2.4
Expected Return on Plan Assets (3.3) (3.3) (6.7) (6.7)
Amortization of Prior Service Credit (0.1) (0.5) (0.2) (0.9)
Amortization of Net Actuarial Gain (Loss) 0.0 0.1 0.0 0.2
Net Periodic Benefit Cost (Credit) (2.3) (2.3) (4.7) (4.7)
OPEB | OPCo        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 0.1 0.1 0.2 0.2
Interest Cost 0.9 1.0 1.7 2.1
Expected Return on Plan Assets (3.0) (2.9) (5.9) (5.9)
Amortization of Prior Service Credit 0.0 (0.3) (0.1) (0.6)
Amortization of Net Actuarial Gain (Loss) 0.0 0.1 0.0 0.2
Net Periodic Benefit Cost (Credit) (2.0) (2.0) (4.1) (4.0)
OPEB | PSO        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 0.1 0.0 0.1 0.1
Interest Cost 0.5 0.6 0.9 1.1
Expected Return on Plan Assets (1.5) (1.6) (3.0) (3.0)
Amortization of Prior Service Credit (0.1) (0.2) (0.1) (0.4)
Amortization of Net Actuarial Gain (Loss) 0.0 0.1 0.0 0.1
Net Periodic Benefit Cost (Credit) (1.0) (1.1) (2.1) (2.1)
OPEB | SWEPCo        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 0.0 0.1 0.1 0.2
Interest Cost 0.6 0.6 1.1 1.3
Expected Return on Plan Assets (1.9) (1.8) (3.8) (3.7)
Amortization of Prior Service Credit (0.1) (0.2) (0.1) (0.5)
Amortization of Net Actuarial Gain (Loss) 0.0 0.0 0.0 0.1
Net Periodic Benefit Cost (Credit) $ (1.4) $ (1.3) $ (2.7) $ (2.6)