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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)

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