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Benefit Plans (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Pension Plans [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | $ 25.6 |  | $ 23.6 | $ 51.2 |  | $ 47.2
Interest Cost | 51.9 |  | 54.8 | 103.8 |  | 109.6
Expected Return on Plan Assets | (80.2) |  | (84.8) | (160.4) |  | (169.6)
Amortization of Net Actuarial Loss | 1.1 |  | 0.4 | 2.2 |  | 0.7
Net Periodic Benefit Cost (Credit) | (1.6) | [1] | (6.0) | (3.2) | [1] | (12.1)
Pension Plans [Member] | AEP Texas Inc. [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 2.2 |  | 2.1 | 4.4 |  | 4.1
Interest Cost | 4.4 |  | 4.6 | 8.7 |  | 9.2
Expected Return on Plan Assets | (6.6) |  | (7.0) | (13.0) |  | (14.0)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.2 |  | 0.0
Net Periodic Benefit Cost (Credit) | 0.1 |  | (0.3) | 0.3 |  | (0.7)
Pension Plans [Member] | Appalachian Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 2.5 |  | 2.2 | 4.9 |  | 4.5
Interest Cost | 6.2 |  | 6.6 | 12.4 |  | 13.2
Expected Return on Plan Assets | (10.7) |  | (11.1) | (21.4) |  | (22.3)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.2 |  | 0.0
Net Periodic Benefit Cost (Credit) | (1.9) |  | (2.3) | (3.9) |  | (4.6)
Pension Plans [Member] | Indiana Michigan Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 3.3 |  | 3.0 | 6.6 |  | 6.0
Interest Cost | 5.9 |  | 6.2 | 11.9 |  | 12.4
Expected Return on Plan Assets | (10.6) |  | (11.1) | (21.4) |  | (22.1)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.2 |  | 0.0
Net Periodic Benefit Cost (Credit) | (1.3) |  | (1.9) | (2.7) |  | (3.7)
Pension Plans [Member] | Ohio Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 2.3 |  | 2.1 | 4.7 |  | 4.2
Interest Cost | 4.7 |  | 5.0 | 9.4 |  | 9.9
Expected Return on Plan Assets | (8.1) |  | (8.5) | (16.3) |  | (17.0)
Amortization of Net Actuarial Loss | 0.0 |  | 0.0 | 0.1 |  | 0.0
Net Periodic Benefit Cost (Credit) | (1.1) |  | (1.4) | (2.1) |  | (2.9)
Pension Plans [Member] | Public Service Co Of Oklahoma [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 1.6 |  | 1.4 | 3.1 |  | 2.8
Interest Cost | 2.5 |  | 2.7 | 5.0 |  | 5.4
Expected Return on Plan Assets | (4.4) |  | (4.6) | (8.7) |  | (9.2)
Amortization of Net Actuarial Loss | 0.1 |  | 0.0 | 0.1 |  | 0.0
Net Periodic Benefit Cost (Credit) | (0.2) |  | (0.5) | (0.5) |  | (1.0)
Pension Plans [Member] | Southwestern Electric Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 2.1 |  | 1.9 | 4.0 |  | 3.8
Interest Cost | 3.1 |  | 3.5 | 6.2 |  | 7.0
Expected Return on Plan Assets | (4.4) |  | (4.9) | (8.8) |  | (9.7)
Amortization of Net Actuarial Loss | 0.0 |  | 0.0 | 0.1 |  | 0.0
Net Periodic Benefit Cost (Credit) | 0.8 |  | 0.5 | 1.5 |  | 1.1
Other Postretirement Benefit Plans [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 1.1 |  | 1.2 | 2.2 |  | 2.3
Interest Cost | 10.6 |  | 11.5 | 21.1 |  | 23.1
Expected Return on Plan Assets | (27.9) |  | (27.4) | (55.7) |  | (54.8)
Amortization of Prior Service Cost (Credit) | (3.2) |  | (15.7) | (6.4) |  | (31.5)
Amortization of Net Actuarial Loss | 0.7 |  | 3.7 | 1.5 |  | 7.4
Net Periodic Benefit Cost (Credit) | (18.7) | [2] | (26.7) | (37.3) | [2] | (53.5)
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.1 |  | 0.1 | 0.2 |  | 0.2
Interest Cost | 0.8 |  | 0.9 | 1.6 |  | 1.8
Expected Return on Plan Assets | (2.2) |  | (2.2) | (4.5) |  | (4.5)
Amortization of Prior Service Cost (Credit) | (0.2) |  | (1.4) | (0.5) |  | (2.7)
Amortization of Net Actuarial Loss | 0.0 |  | 0.3 | 0.1 |  | 0.6
Net Periodic Benefit Cost (Credit) | (1.5) | [2] | (2.3) | (3.1) | [2] | (4.6)
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.1 |  | 0.2 | 0.2 |  | 0.3
Interest Cost | 1.6 |  | 1.9 | 3.3 |  | 3.7
Expected Return on Plan Assets | (4.1) |  | (4.0) | (8.1) |  | (8.0)
Amortization of Prior Service Cost (Credit) | (0.4) |  | (2.3) | (0.9) |  | (4.6)
Amortization of Net Actuarial Loss | 0.1 |  | 0.5 | 0.2 |  | 1.1
Net Periodic Benefit Cost (Credit) | (2.7) | [2] | (3.7) | (5.3) | [2] | (7.5)
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.2 |  | 0.2 | 0.3 |  | 0.4
Interest Cost | 1.2 |  | 1.4 | 2.4 |  | 2.7
Expected Return on Plan Assets | (3.3) |  | (3.4) | (6.7) |  | (6.8)
Amortization of Prior Service Cost (Credit) | (0.5) |  | (2.1) | (0.9) |  | (4.3)
Amortization of Net Actuarial Loss | 0.1 |  | 0.4 | 0.2 |  | 0.9
Net Periodic Benefit Cost (Credit) | (2.3) | [2] | (3.5) | (4.7) | [2] | (7.1)
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.1 |  | 0.1 | 0.2 |  | 0.2
Interest Cost | 1.0 |  | 1.1 | 2.1 |  | 2.3
Expected Return on Plan Assets | (2.9) |  | (3.0) | (5.9) |  | (5.9)
Amortization of Prior Service Cost (Credit) | (0.3) |  | (1.5) | (0.6) |  | (3.1)
Amortization of Net Actuarial Loss | 0.1 |  | 0.4 | 0.2 |  | 0.8
Net Periodic Benefit Cost (Credit) | (2.0) | [2] | (2.9) | (4.0) | [2] | (5.7)
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.0 |  | 0.0 | 0.1 |  | 0.1
Interest Cost | 0.6 |  | 0.6 | 1.1 |  | 1.2
Expected Return on Plan Assets | (1.6) |  | (1.4) | (3.0) |  | (2.9)
Amortization of Prior Service Cost (Credit) | (0.2) |  | (1.0) | (0.4) |  | (2.0)
Amortization of Net Actuarial Loss | 0.1 |  | 0.2 | 0.1 |  | 0.4
Net Periodic Benefit Cost (Credit) | (1.1) | [2] | (1.6) | (2.1) | [2] | (3.2)
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member] |  |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 0.1 |  | 0.1 | 0.2 |  | 0.2
Interest Cost | 0.6 |  | 0.7 | 1.3 |  | 1.4
Expected Return on Plan Assets | (1.8) |  | (1.8) | (3.7) |  | (3.6)
Amortization of Prior Service Cost (Credit) | (0.2) |  | (1.2) | (0.5) |  | (2.4)
Amortization of Net Actuarial Loss | 0.0 |  | 0.3 | 0.1 |  | 0.5
Net Periodic Benefit Cost (Credit) | $ (1.3) | [2] | $ (1.9) | $ (2.6) | [2] | $ (3.9)
[1] | Excludes an immaterial one-time settlement cost to a non-qualified pension plan in the second quarter of 2024 for AEP.
[2] | Excludes an immaterial one-time cost 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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