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Benefit Plans (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Pension Plans [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | $ 25.6 |  | $ 23.6 | $ 76.8 |  | $ 70.8
Interest Cost | 51.9 |  | 54.8 | 155.7 |  | 164.4
Expected Return on Plan Assets | (80.2) |  | (84.8) | (240.6) |  | (254.4)
Amortization of Net Actuarial Loss | 1.0 |  | 0.3 | 3.2 |  | 1.0
Net Periodic Benefit Cost (Credit) | (1.7) | [1] | (6.1) | (4.9) | [1] | (18.2)
Pension Plans [Member] | AEP Texas Inc. [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 2.3 |  | 2.1 | 6.7 |  | 6.2
Interest Cost | 4.4 |  | 4.5 | 13.1 |  | 13.7
Expected Return on Plan Assets | (6.5) |  | (7.0) | (19.5) |  | (21.0)
Amortization of Net Actuarial Loss | 0.0 |  | 0.0 | 0.2 |  | 0.0
Net Periodic Benefit Cost (Credit) | 0.2 |  | (0.4) | 0.5 |  | (1.1)
Pension Plans [Member] | Appalachian Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 2.4 |  | 2.3 | 7.3 |  | 6.8
Interest Cost | 6.2 |  | 6.6 | 18.6 |  | 19.8
Expected Return on Plan Assets | (10.7) |  | (11.2) | (32.1) |  | (33.5)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.3 |  | 0.0
Net Periodic Benefit Cost (Credit) | (2.0) |  | (2.3) | (5.9) |  | (6.9)
Pension Plans [Member] | Indiana Michigan Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 3.3 |  | 2.9 | 9.9 |  | 8.9
Interest Cost | 5.9 |  | 6.3 | 17.8 |  | 18.7
Expected Return on Plan Assets | (10.7) |  | (11.0) | (32.1) |  | (33.1)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.3 |  | 0.0
Net Periodic Benefit Cost (Credit) | (1.4) |  | (1.8) | (4.1) |  | (5.5)
Pension Plans [Member] | Ohio Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 2.3 |  | 2.1 | 7.0 |  | 6.3
Interest Cost | 4.8 |  | 5.0 | 14.2 |  | 14.9
Expected Return on Plan Assets | (8.2) |  | (8.6) | (24.5) |  | (25.6)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.2 |  | 0.0
Net Periodic Benefit Cost (Credit) | (1.0) |  | (1.5) | (3.1) |  | (4.4)
Pension Plans [Member] | Public Service Co Of Oklahoma [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 1.5 |  | 1.4 | 4.6 |  | 4.2
Interest Cost | 2.5 |  | 2.7 | 7.5 |  | 8.1
Expected Return on Plan Assets | (4.3) |  | (4.6) | (13.0) |  | (13.8)
Amortization of Net Actuarial Loss | 0.0 |  | 0.0 | 0.1 |  | 0.0
Net Periodic Benefit Cost (Credit) | (0.3) |  | (0.5) | (0.8) |  | (1.5)
Pension Plans [Member] | Southwestern Electric Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 1.9 |  | 2.0 | 5.9 |  | 5.8
Interest Cost | 3.1 |  | 3.4 | 9.3 |  | 10.4
Expected Return on Plan Assets | (4.4) |  | (4.8) | (13.2) |  | (14.5)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.2 |  | 0.0
Net Periodic Benefit Cost (Credit) | 0.7 |  | 0.6 | 2.2 |  | 1.7
Other Postretirement Benefit Plans [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 1.1 |  | 1.1 | 3.3 |  | 3.4
Interest Cost | 10.3 |  | 11.6 | 31.4 |  | 34.7
Expected Return on Plan Assets | (27.8) |  | (27.4) | (83.5) |  | (82.2)
Amortization of Prior Service Cost (Credit) | (3.1) |  | (15.8) | (9.5) |  | (47.3)
Amortization of Net Actuarial Loss | 0.8 |  | 3.7 | 2.3 |  | 11.1
Net Periodic Benefit Cost (Credit) | (18.7) | [2] | (26.8) | (56.0) | [2] | (80.3)
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.0 |  | 0.1 | 0.2 |  | 0.3
Interest Cost | 0.9 |  | 0.9 | 2.5 |  | 2.7
Expected Return on Plan Assets | (2.3) |  | (2.2) | (6.8) |  | (6.7)
Amortization of Prior Service Cost (Credit) | (0.3) |  | (1.3) | (0.8) |  | (4.0)
Amortization of Net Actuarial Loss | 0.1 |  | 0.3 | 0.2 |  | 0.9
Net Periodic Benefit Cost (Credit) | (1.6) | [2] | (2.2) | (4.7) | [2] | (6.8)
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.2 |  | 0.1 | 0.4 |  | 0.4
Interest Cost | 1.7 |  | 1.8 | 5.0 |  | 5.5
Expected Return on Plan Assets | (4.1) |  | (4.0) | (12.2) |  | (12.0)
Amortization of Prior Service Cost (Credit) | (0.5) |  | (2.3) | (1.4) |  | (6.9)
Amortization of Net Actuarial Loss | 0.1 |  | 0.6 | 0.3 |  | 1.7
Net Periodic Benefit Cost (Credit) | (2.6) | [2] | (3.8) | (7.9) | [2] | (11.3)
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.1 |  | 0.1 | 0.4 |  | 0.5
Interest Cost | 1.2 |  | 1.3 | 3.6 |  | 4.0
Expected Return on Plan Assets | (3.4) |  | (3.3) | (10.1) |  | (10.1)
Amortization of Prior Service Cost (Credit) | (0.4) |  | (2.2) | (1.3) |  | (6.5)
Amortization of Net Actuarial Loss | 0.1 |  | 0.5 | 0.3 |  | 1.4
Net Periodic Benefit Cost (Credit) | (2.4) | [2] | (3.6) | (7.1) | [2] | (10.7)
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.0 |  | 0.1 | 0.2 |  | 0.3
Interest Cost | 1.1 |  | 1.2 | 3.2 |  | 3.5
Expected Return on Plan Assets | (3.0) |  | (2.9) | (8.9) |  | (8.8)
Amortization of Prior Service Cost (Credit) | (0.3) |  | (1.6) | (0.9) |  | (4.7)
Amortization of Net Actuarial Loss | 0.1 |  | 0.4 | 0.3 |  | 1.2
Net Periodic Benefit Cost (Credit) | (2.1) | [2] | (2.8) | (6.1) | [2] | (8.5)
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.1 |  | 0.1 | 0.2 |  | 0.2
Interest Cost | 0.6 |  | 0.6 | 1.7 |  | 1.8
Expected Return on Plan Assets | (1.5) |  | (1.5) | (4.5) |  | (4.4)
Amortization of Prior Service Cost (Credit) | (0.2) |  | (1.0) | (0.6) |  | (3.0)
Amortization of Net Actuarial Loss | 0.0 |  | 0.2 | 0.1 |  | 0.6
Net Periodic Benefit Cost (Credit) | (1.0) | [2] | (1.6) | (3.1) | [2] | (4.8)
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.1 |  | 0.0 | 0.3 |  | 0.2
Interest Cost | 0.7 |  | 0.8 | 2.0 |  | 2.2
Expected Return on Plan Assets | (1.9) |  | (1.8) | (5.6) |  | (5.4)
Amortization of Prior Service Cost (Credit) | (0.3) |  | (1.3) | (0.8) |  | (3.7)
Amortization of Net Actuarial Loss | 0.1 |  | 0.3 | 0.2 |  | 0.8
Net Periodic Benefit Cost (Credit) | $ (1.3) | [2] | $ (2.0) | $ (3.9) | [2] | $ (5.9)
[1] | Excludes an immaterial settlement amount to a non-qualified pension plan in the second quarter of 2024 for AEP. Management continues to monitor settlements under the qualified pension plan as a result of the voluntary severance program announced in the second quarter of 2024. See Note 13 - Voluntary Severance Program for additional information.
[2] | Excludes an immaterial amount related to special termination benefits resulting from the voluntary severance program announced in the second quarter of 2024. See Note 13 - Voluntary Severance Program for additional information.

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