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Benefit Plans (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Pension Plans [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | $ 23.6 | $ 30.7 | $ 70.8 | $ 92.3
Interest Cost | 54.8 | 37.1 | 164.4 | 111.2
Expected Return on Plan Assets | (84.8) | (63.4) | (254.4) | (190.1)
Amortization of Net Actuarial Loss | 0.3 | 15.8 | 1.0 | 47.3
Net Periodic Benefit Cost (Credit) | (6.1) | 20.2 | (18.2) | 60.7
Pension Plans [Member] | AEP Texas Inc. [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 2.1 | 2.8 | 6.2 | 8.4
Interest Cost | 4.5 | 3.1 | 13.7 | 9.1
Expected Return on Plan Assets | (7.0) | (5.3) | (21.0) | (15.8)
Amortization of Net Actuarial Loss | 0.0 | 1.2 | 0.0 | 3.8
Net Periodic Benefit Cost (Credit) | (0.4) | 1.8 | (1.1) | 5.5
Pension Plans [Member] | Appalachian Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 2.3 | 2.9 | 6.8 | 8.6
Interest Cost | 6.6 | 4.3 | 19.8 | 13.1
Expected Return on Plan Assets | (11.2) | (8.1) | (33.5) | (24.3)
Amortization of Net Actuarial Loss | 0.0 | 1.9 | 0.0 | 5.5
Net Periodic Benefit Cost (Credit) | (2.3) | 1.0 | (6.9) | 2.9
Pension Plans [Member] | Indiana Michigan Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 2.9 | 4.0 | 8.9 | 12.1
Interest Cost | 6.3 | 4.3 | 18.7 | 12.7
Expected Return on Plan Assets | (11.0) | (8.1) | (33.1) | (24.2)
Amortization of Net Actuarial Loss | 0.0 | 1.8 | 0.0 | 5.3
Net Periodic Benefit Cost (Credit) | (1.8) | 2.0 | (5.5) | 5.9
Pension Plans [Member] | Ohio Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 2.1 | 2.8 | 6.3 | 8.4
Interest Cost | 5.0 | 3.4 | 14.9 | 10.0
Expected Return on Plan Assets | (8.6) | (6.2) | (25.6) | (18.6)
Amortization of Net Actuarial Loss | 0.0 | 1.3 | 0.0 | 4.1
Net Periodic Benefit Cost (Credit) | (1.5) | 1.3 | (4.4) | 3.9
Pension Plans [Member] | Public Service Co Of Oklahoma [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 1.4 | 1.8 | 4.2 | 5.5
Interest Cost | 2.7 | 1.8 | 8.1 | 5.3
Expected Return on Plan Assets | (4.6) | (3.3) | (13.8) | (10.1)
Amortization of Net Actuarial Loss | 0.0 | 0.7 | 0.0 | 2.2
Net Periodic Benefit Cost (Credit) | (0.5) | 1.0 | (1.5) | 2.9
Pension Plans [Member] | Southwestern Electric Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 2.0 | 2.7 | 5.8 | 8.0
Interest Cost | 3.4 | 2.2 | 10.4 | 6.8
Expected Return on Plan Assets | (4.8) | (3.6) | (14.5) | (10.9)
Amortization of Net Actuarial Loss | 0.0 | 0.9 | 0.0 | 2.8
Net Periodic Benefit Cost (Credit) | 0.6 | 2.2 | 1.7 | 6.7
Other Postretirement Benefit Plans [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 1.1 | 1.8 | 3.4 | 5.5
Interest Cost | 11.6 | 7.3 | 34.7 | 21.9
Expected Return on Plan Assets | (27.4) | (27.5) | (82.2) | (82.5)
Amortization of Prior Service Cost (Credit) | (15.8) | (17.9) | (47.3) | (53.6)
Amortization of Net Actuarial Loss | 3.7 |  | 11.1 |
Net Periodic Benefit Cost (Credit) | (26.8) | (36.3) | (80.3) | (108.7)
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 0.1 | 0.1 | 0.3 | 0.3
Interest Cost | 0.9 | 0.6 | 2.7 | 1.7
Expected Return on Plan Assets | (2.2) | (2.3) | (6.7) | (6.8)
Amortization of Prior Service Cost (Credit) | (1.3) | (1.5) | (4.0) | (4.5)
Amortization of Net Actuarial Loss | 0.3 |  | 0.9 |
Net Periodic Benefit Cost (Credit) | (2.2) | (3.1) | (6.8) | (9.3)
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 0.1 | 0.2 | 0.4 | 0.6
Interest Cost | 1.8 | 1.2 | 5.5 | 3.5
Expected Return on Plan Assets | (4.0) | (4.1) | (12.0) | (12.2)
Amortization of Prior Service Cost (Credit) | (2.3) | (2.6) | (6.9) | (7.8)
Amortization of Net Actuarial Loss | 0.6 |  | 1.7 |
Net Periodic Benefit Cost (Credit) | (3.8) | (5.3) | (11.3) | (15.9)
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 0.1 | 0.2 | 0.5 | 0.7
Interest Cost | 1.3 | 0.8 | 4.0 | 2.5
Expected Return on Plan Assets | (3.3) | (3.3) | (10.1) | (10.2)
Amortization of Prior Service Cost (Credit) | (2.2) | (2.4) | (6.5) | (7.3)
Amortization of Net Actuarial Loss | 0.5 |  | 1.4 |
Net Periodic Benefit Cost (Credit) | (3.6) | (4.7) | (10.7) | (14.3)
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 0.1 | 0.2 | 0.3 | 0.5
Interest Cost | 1.2 | 0.7 | 3.5 | 2.2
Expected Return on Plan Assets | (2.9) | (3.0) | (8.8) | (8.9)
Amortization of Prior Service Cost (Credit) | (1.6) | (1.8) | (4.7) | (5.4)
Amortization of Net Actuarial Loss | 0.4 |  | 1.2 |
Net Periodic Benefit Cost (Credit) | (2.8) | (3.9) | (8.5) | (11.6)
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 0.1 | 0.2 | 0.2 | 0.4
Interest Cost | 0.6 | 0.4 | 1.8 | 1.1
Expected Return on Plan Assets | (1.5) | (1.6) | (4.4) | (4.6)
Amortization of Prior Service Cost (Credit) | (1.0) | (1.1) | (3.0) | (3.3)
Amortization of Net Actuarial Loss | 0.2 |  | 0.6 |
Net Periodic Benefit Cost (Credit) | (1.6) | (2.1) | (4.8) | (6.4)
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service Cost | 0.0 | 0.1 | 0.2 | 0.4
Interest Cost | 0.8 | 0.5 | 2.2 | 1.4
Expected Return on Plan Assets | (1.8) | (1.8) | (5.4) | (5.5)
Amortization of Prior Service Cost (Credit) | (1.3) | (1.4) | (3.7) | (4.0)
Amortization of Net Actuarial Loss | 0.3 |  | 0.8 |
Net Periodic Benefit Cost (Credit) | $ (2.0) | $ (2.6) | $ (5.9) | $ (7.7)

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