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Benefit Plans 3 (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 76.4 $ 71.8 $ 74.6
Benefit Plans Textuals [Abstract]      
Matching Contributions Provided Percentage 100.00%    
Eligible Compensation Contribution by Employee Percentage 1.00%    
Second Matching Contributions Provided Percentage 70.00%    
Second Eligible Compensation Contribution by Employee Percentage 5.00%    
Multiemployer Plans Withdrawal Obligation $ 20.0 15.0  
Noncurrent Regulatory Assets 3,158.8 3,310.4  
Noncurrent Regulatory Liabilities 8,457.6 8,540.3  
UMWA Withdrawal Obligation [Member]      
Benefit Plans Textuals [Abstract]      
Noncurrent Regulatory Assets 2.0    
Noncurrent Regulatory Liabilities   3.0  
AEP Texas Inc. [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 5.9 5.7 6.0
Benefit Plans Textuals [Abstract]      
Matching Contributions Provided Percentage 100.00%    
Eligible Compensation Contribution by Employee Percentage 1.00%    
Second Matching Contributions Provided Percentage 70.00%    
Second Eligible Compensation Contribution by Employee Percentage 5.00%    
Noncurrent Regulatory Assets $ 280.6 430.0  
Noncurrent Regulatory Liabilities 1,316.9 1,344.3  
Appalachian Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 7.5 7.5 7.4
Benefit Plans Textuals [Abstract]      
Matching Contributions Provided Percentage 100.00%    
Eligible Compensation Contribution by Employee Percentage 1.00%    
Second Matching Contributions Provided Percentage 70.00%    
Second Eligible Compensation Contribution by Employee Percentage 5.00%    
Noncurrent Regulatory Assets $ 457.2 475.8  
Noncurrent Regulatory Liabilities 1,268.7 1,449.7  
Indiana Michigan Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 11.0 10.5 10.7
Benefit Plans Textuals [Abstract]      
Matching Contributions Provided Percentage 100.00%    
Eligible Compensation Contribution by Employee Percentage 1.00%    
Second Matching Contributions Provided Percentage 70.00%    
Second Eligible Compensation Contribution by Employee Percentage 5.00%    
Noncurrent Regulatory Assets $ 482.1 512.5  
Noncurrent Regulatory Liabilities 1,891.4 1,574.5  
Ohio Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 6.6 6.3 6.1
Benefit Plans Textuals [Abstract]      
Matching Contributions Provided Percentage 100.00%    
Eligible Compensation Contribution by Employee Percentage 1.00%    
Second Matching Contributions Provided Percentage 70.00%    
Second Eligible Compensation Contribution by Employee Percentage 5.00%    
Noncurrent Regulatory Assets $ 351.8 387.5  
Noncurrent Regulatory Liabilities 1,090.9 1,221.2  
Public Service Co Of Oklahoma [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 4.6 4.5 5.0
Benefit Plans Textuals [Abstract]      
Matching Contributions Provided Percentage 100.00%    
Eligible Compensation Contribution by Employee Percentage 1.00%    
Second Matching Contributions Provided Percentage 70.00%    
Second Eligible Compensation Contribution by Employee Percentage 5.00%    
Noncurrent Regulatory Assets $ 375.2 369.0  
Noncurrent Regulatory Liabilities 837.2 864.7  
Southwestern Electric Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 6.2 5.9 6.0
Benefit Plans Textuals [Abstract]      
Matching Contributions Provided Percentage 100.00%    
Eligible Compensation Contribution by Employee Percentage 1.00%    
Second Matching Contributions Provided Percentage 70.00%    
Second Eligible Compensation Contribution by Employee Percentage 5.00%    
Noncurrent Regulatory Assets $ 222.4 230.8  
Noncurrent Regulatory Liabilities 892.3 923.0  
Pension Plans [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 4,998.7 4,625.6  
Underfunded Benefit Obligation      
Projected Benefit Obligation 5,236.8 4,810.3 5,215.8
Accumulated Benefit Obligation 4,998.7 4,625.6  
Fair Value of Plan Assets 5,015.4 4,695.9 5,174.1
Underfunded Status, Projected Benefit Obligation (221.4) (114.4)  
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 6.1    
Components of Net Periodic Benefit Cost      
Service Cost 95.5 97.6 96.5
Interest Cost 204.4 187.8 203.1
Expected Return on Plan Assets (296.0) (290.3) (284.8)
Amortization of Prior Service Cost (Credit) 0.0 0.0 1.0
Amortization of Net Actuarial Loss 57.6 85.2 82.8
Settlements 0.0 2.6 0.0
Net Periodic Benefit Cost (Credit) 61.5 82.9 98.6
Capitalized Portion (38.6) (41.1) (39.9)
Net Periodic Benefit Cost (Credit) Recognized in Expense 22.9 41.8 58.7
Pension Plans [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 378.1    
2021 382.8    
2022 380.5    
2023 383.8    
2024 382.9    
Years 2025 to 2029, in Total 1,800.7    
Pension Plans [Member] | AEP Texas Inc. [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 421.1 396.8  
Underfunded Benefit Obligation      
Projected Benefit Obligation 441.2 409.3 441.3
Accumulated Benefit Obligation 421.1 396.8  
Fair Value of Plan Assets 435.1 410.7 455.9
Underfunded Status, Projected Benefit Obligation (6.1)    
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.4    
Components of Net Periodic Benefit Cost      
Service Cost 8.6 9.2 8.6
Interest Cost 17.5 16.0 17.1
Expected Return on Plan Assets (25.8) (25.6) (25.0)
Amortization of Prior Service Cost (Credit) 0.0 0.0 0.0
Amortization of Net Actuarial Loss 4.9 7.2 7.0
Net Periodic Benefit Cost (Credit) 5.2 6.8 7.7
Capitalized Portion (4.5) (4.8) (4.0)
Net Periodic Benefit Cost (Credit) Recognized in Expense 0.7 2.0 3.7
Pension Plans [Member] | AEP Texas Inc. [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 37.5    
2021 37.3    
2022 35.9    
2023 36.6    
2024 36.3    
Years 2025 to 2029, in Total 162.2    
Pension Plans [Member] | Appalachian Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 627.5 588.5  
Underfunded Benefit Obligation      
Projected Benefit Obligation 647.2 603.1 665.0
Accumulated Benefit Obligation 627.5 588.5  
Fair Value of Plan Assets 637.0 593.3 651.7
Underfunded Status, Projected Benefit Obligation (10.2) (9.8)  
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 9.4 9.3 9.4
Interest Cost 25.2 23.5 25.7
Expected Return on Plan Assets (37.4) (36.6) (35.8)
Amortization of Prior Service Cost (Credit) 0.0 0.0 0.2
Amortization of Net Actuarial Loss 7.0 10.6 10.4
Net Periodic Benefit Cost (Credit) 4.2 6.8 9.9
Capitalized Portion (4.0) (3.8) (4.0)
Net Periodic Benefit Cost (Credit) Recognized in Expense 0.2 3.0 5.9
Pension Plans [Member] | Appalachian Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 45.8    
2021 46.0    
2022 45.7    
2023 46.1    
2024 46.8    
Years 2025 to 2029, in Total 217.4    
Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 586.9 536.9  
Underfunded Benefit Obligation      
Projected Benefit Obligation 616.1 567.0 624.3
Accumulated Benefit Obligation 586.9 536.9  
Fair Value of Plan Assets 630.5 583.8 636.7
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 13.4 13.6 14.0
Interest Cost 23.8 22.1 24.3
Expected Return on Plan Assets (36.8) (35.7) (34.6)
Amortization of Prior Service Cost (Credit) 0.0 0.0 0.2
Amortization of Net Actuarial Loss 6.6 9.8 9.7
Net Periodic Benefit Cost (Credit) 7.0 9.8 13.6
Capitalized Portion (3.4) (5.6) (5.5)
Net Periodic Benefit Cost (Credit) Recognized in Expense 3.6 4.2 8.1
Pension Plans [Member] | Indiana Michigan Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 40.1    
2021 40.5    
2022 42.5    
2023 42.2    
2024 42.8    
Years 2025 to 2029, in Total 211.6    
Pension Plans [Member] | Ohio Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 464.3 438.5  
Underfunded Benefit Obligation      
Projected Benefit Obligation 487.8 453.9 501.1
Accumulated Benefit Obligation 464.3 438.5  
Fair Value of Plan Assets 499.1 466.1 509.1
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 7.9 7.7 7.5
Interest Cost 19.1 17.7 19.4
Expected Return on Plan Assets (29.3) (28.8) (27.9)
Amortization of Prior Service Cost (Credit) 0.0 0.0 0.1
Amortization of Net Actuarial Loss 5.3 8.0 7.8
Net Periodic Benefit Cost (Credit) 3.0 4.6 6.9
Capitalized Portion (3.7) (3.6) (3.3)
Net Periodic Benefit Cost (Credit) Recognized in Expense (0.7) 1.0 3.6
Pension Plans [Member] | Ohio Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 36.2    
2021 36.1    
2022 35.7    
2023 35.8    
2024 34.0    
Years 2025 to 2029, in Total 161.1    
Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 250.5 240.2  
Underfunded Benefit Obligation      
Projected Benefit Obligation 267.5 253.8 276.6
Accumulated Benefit Obligation 250.5 240.2  
Fair Value of Plan Assets 276.2 261.2 287.8
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.1    
Components of Net Periodic Benefit Cost      
Service Cost 6.5 7.0 6.4
Interest Cost 10.6 9.9 10.7
Expected Return on Plan Assets (16.3) (16.1) (15.6)
Amortization of Prior Service Cost (Credit) 0.0 0.0 0.0
Amortization of Net Actuarial Loss 2.9 4.4 4.3
Net Periodic Benefit Cost (Credit) 3.7 5.2 5.8
Capitalized Portion (2.4) (2.6) (2.1)
Net Periodic Benefit Cost (Credit) Recognized in Expense 1.3 2.6 3.7
Pension Plans [Member] | Public Service Co Of Oklahoma [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 20.9    
2021 21.3    
2022 21.2    
2023 22.6    
2024 21.5    
Years 2025 to 2029, in Total 98.3    
Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 293.2 272.8  
Underfunded Benefit Obligation      
Projected Benefit Obligation 314.2 291.4 314.6
Accumulated Benefit Obligation 293.2 272.8  
Fair Value of Plan Assets 296.9 281.0 311.7
Underfunded Status, Projected Benefit Obligation (17.3) (10.4)  
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.1    
Components of Net Periodic Benefit Cost      
Service Cost 8.6 9.3 8.7
Interest Cost 12.4 11.3 12.3
Expected Return on Plan Assets (17.7) (17.3) (17.0)
Amortization of Prior Service Cost (Credit) 0.0 0.0 0.1
Amortization of Net Actuarial Loss 3.4 5.1 4.9
Settlements 0.0 0.4 0.0
Net Periodic Benefit Cost (Credit) 6.7 8.8 9.0
Capitalized Portion (2.9) (3.1) (2.7)
Net Periodic Benefit Cost (Credit) Recognized in Expense 3.8 5.7 6.3
Pension Plans [Member] | Southwestern Electric Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 24.0    
2021 24.7    
2022 25.2    
2023 25.4    
2024 25.8    
Years 2025 to 2029, in Total 119.6    
Qualified Pension Plans [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 4,929.0 4,560.7  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 4,929.0 4,560.7  
Qualified Pension Plans [Member] | AEP Texas Inc. [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 417.5 393.2  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 417.5 393.2  
Qualified Pension Plans [Member] | Appalachian Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 627.3 588.3  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 627.3 588.3  
Qualified Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 586.3 536.3  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 586.3 536.3  
Qualified Pension Plans [Member] | Ohio Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 464.2 438.3  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 464.2 438.3  
Qualified Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 248.9 238.0  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 248.9 238.0  
Qualified Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 291.9 271.6  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 291.9 271.6  
Nonqualified Pension Plans [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 69.7 64.9  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 69.7 64.9  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Accumulated Benefit Obligation (69.7) (64.9)  
Nonqualified Pension Plans [Member] | AEP Texas Inc. [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 3.6 3.6  
Underfunded Benefit Obligation      
Projected Benefit Obligation   3.8  
Accumulated Benefit Obligation 3.6 3.6  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Projected Benefit Obligation   (3.8)  
Underfunded Status, Accumulated Benefit Obligation (3.6) (3.6)  
Nonqualified Pension Plans [Member] | Appalachian Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.2 0.2  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 0.2 0.2  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Accumulated Benefit Obligation (0.2) (0.2)  
Nonqualified Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.6 0.6  
Underfunded Benefit Obligation      
Projected Benefit Obligation 1.5 1.2  
Accumulated Benefit Obligation 0.6 0.6  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Projected Benefit Obligation (1.5) (1.2)  
Underfunded Status, Accumulated Benefit Obligation (0.6) (0.6)  
Nonqualified Pension Plans [Member] | Ohio Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.1 0.2  
Underfunded Benefit Obligation      
Projected Benefit Obligation 0.4 0.4  
Accumulated Benefit Obligation 0.1 0.2  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Projected Benefit Obligation (0.4) (0.4)  
Underfunded Status, Accumulated Benefit Obligation (0.1) (0.2)  
Nonqualified Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 1.6 2.2  
Underfunded Benefit Obligation      
Projected Benefit Obligation 1.9 2.3  
Accumulated Benefit Obligation 1.6 2.2  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Projected Benefit Obligation (1.9) (2.3)  
Underfunded Status, Accumulated Benefit Obligation (1.6) (2.2)  
Nonqualified Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 1.3 1.2  
Underfunded Benefit Obligation      
Accumulated Benefit Obligation 1.3 1.2  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Accumulated Benefit Obligation (1.3) (1.2)  
Other Postretirement Benefit Plans [Member]      
Underfunded Benefit Obligation      
Projected Benefit Obligation 1,225.4 1,194.5 1,332.0
Fair Value of Plan Assets 1,781.8 1,534.2 1,732.5
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 3.4    
Components of Net Periodic Benefit Cost      
Service Cost 9.5 11.6 11.2
Interest Cost 50.5 47.4 59.3
Expected Return on Plan Assets (93.7) (102.2) (101.3)
Amortization of Prior Service Cost (Credit) (69.1) (69.1) (69.1)
Amortization of Net Actuarial Loss 22.1 10.5 36.7
Settlements 0.0 0.0 0.0
Net Periodic Benefit Cost (Credit) (80.7) (101.8) (63.2)
Capitalized Portion (3.8) (4.9) 25.6
Net Periodic Benefit Cost (Credit) Recognized in Expense (84.5) (106.7) (37.6)
Other Postretirement Benefit Plans [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 126.3    
2021 124.0    
2022 125.2    
2023 125.0    
2024 124.6    
Years 2025 to 2029, in Total 592.6    
Other Postretirement Benefit Plans [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2020 0.2    
2021 0.3    
2022 0.3    
2023 0.3    
2024 0.3    
Years 2025 to 2029, in Total 1.4    
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member]      
Underfunded Benefit Obligation      
Projected Benefit Obligation 97.8 95.9 107.1
Fair Value of Plan Assets 148.1 129.9 147.3
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.1    
Components of Net Periodic Benefit Cost      
Service Cost 0.8 0.9 0.9
Interest Cost 4.0 3.8 4.9
Expected Return on Plan Assets (7.8) (8.6) (8.8)
Amortization of Prior Service Cost (Credit) (5.9) (5.9) (5.8)
Amortization of Net Actuarial Loss 1.8 0.8 3.2
Net Periodic Benefit Cost (Credit) (7.1) (9.0) (5.6)
Capitalized Portion (0.4) (0.5) 2.9
Net Periodic Benefit Cost (Credit) Recognized in Expense (7.5) (9.5) (2.7)
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 10.0    
2021 10.0    
2022 10.4    
2023 10.6    
2024 10.7    
Years 2025 to 2029, in Total 50.8    
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2020 0.0    
2021 0.0    
2022 0.0    
2023 0.0    
2024 0.0    
Years 2025 to 2029, in Total 0.0    
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Underfunded Benefit Obligation      
Projected Benefit Obligation 203.5 205.5 236.5
Fair Value of Plan Assets 271.0 238.4 273.4
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 2.0    
Components of Net Periodic Benefit Cost      
Service Cost 1.0 1.1 1.1
Interest Cost 8.7 8.2 10.6
Expected Return on Plan Assets (14.6) (16.0) (16.5)
Amortization of Prior Service Cost (Credit) (10.1) (10.0) (10.1)
Amortization of Net Actuarial Loss 3.7 1.9 6.3
Net Periodic Benefit Cost (Credit) (11.3) (14.8) (8.6)
Capitalized Portion (0.4) (0.5) 3.5
Net Periodic Benefit Cost (Credit) Recognized in Expense (11.7) (15.3) (5.1)
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 22.5    
2021 21.8    
2022 21.6    
2023 21.2    
2024 21.1    
Years 2025 to 2029, in Total 97.8    
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2020 0.1    
2021 0.2    
2022 0.2    
2023 0.1    
2024 0.1    
Years 2025 to 2029, in Total 0.6    
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Underfunded Benefit Obligation      
Projected Benefit Obligation 142.9 138.3 153.5
Fair Value of Plan Assets 216.3 187.3 211.1
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 1.4 1.6 1.6
Interest Cost 5.8 5.4 6.9
Expected Return on Plan Assets (11.4) (12.3) (12.2)
Amortization of Prior Service Cost (Credit) (9.4) (9.5) (9.4)
Amortization of Net Actuarial Loss 2.7 1.2 4.4
Net Periodic Benefit Cost (Credit) (10.9) (13.6) (8.7)
Capitalized Portion (0.4) (0.7) 3.5
Net Periodic Benefit Cost (Credit) Recognized in Expense (11.3) (14.3) (5.2)
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 15.2    
2021 15.2    
2022 15.5    
2023 15.5    
2024 15.4    
Years 2025 to 2029, in Total 72.8    
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2020 0.0    
2021 0.0    
2022 0.0    
2023 0.0    
2024 0.0    
Years 2025 to 2029, in Total 0.0    
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Underfunded Benefit Obligation      
Projected Benefit Obligation 130.2 129.5 144.3
Fair Value of Plan Assets 197.1 175.4 198.5
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 0.8 0.9 0.9
Interest Cost 5.5 5.1 6.7
Expected Return on Plan Assets (10.8) (11.7) (11.9)
Amortization of Prior Service Cost (Credit) (6.9) (6.9) (6.9)
Amortization of Net Actuarial Loss 2.5 1.1 4.3
Net Periodic Benefit Cost (Credit) (8.9) (11.5) (6.9)
Capitalized Portion (0.4) (0.4) 3.3
Net Periodic Benefit Cost (Credit) Recognized in Expense (9.3) (11.9) (3.6)
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 14.8    
2021 14.2    
2022 14.4    
2023 14.3    
2024 14.1    
Years 2025 to 2029, in Total 65.4    
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2020 0.0    
2021 0.0    
2022 0.0    
2023 0.0    
2024 0.0    
Years 2025 to 2029, in Total 0.0    
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Underfunded Benefit Obligation      
Projected Benefit Obligation 64.7 62.3 69.4
Fair Value of Plan Assets 98.0 84.3 95.5
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 0.6 0.7 0.7
Interest Cost 2.6 2.5 3.2
Expected Return on Plan Assets (5.1) (5.6) (5.6)
Amortization of Prior Service Cost (Credit) (4.3) (4.3) (4.3)
Amortization of Net Actuarial Loss 1.2 0.5 2.0
Net Periodic Benefit Cost (Credit) (5.0) (6.2) (4.0)
Capitalized Portion (0.2) (0.3) 1.4
Net Periodic Benefit Cost (Credit) Recognized in Expense (5.2) (6.5) (2.6)
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 6.8    
2021 6.7    
2022 6.9    
2023 7.0    
2024 7.1    
Years 2025 to 2029, in Total 33.7    
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2020 0.0    
2021 0.0    
2022 0.0    
2023 0.0    
2024 0.0    
Years 2025 to 2029, in Total 0.0    
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Underfunded Benefit Obligation      
Projected Benefit Obligation 77.4 72.7 80.3
Fair Value of Plan Assets 117.2 98.5 110.4
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2020 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 0.8 0.9 0.9
Interest Cost 3.1 2.8 3.6
Expected Return on Plan Assets (5.9) (6.4) (6.3)
Amortization of Prior Service Cost (Credit) (5.2) (5.2) (5.2)
Amortization of Net Actuarial Loss 1.4 0.6 2.3
Settlements 0.0 0.0 0.0
Net Periodic Benefit Cost (Credit) (5.8) (7.3) (4.7)
Capitalized Portion (0.3) (0.3) 1.4
Net Periodic Benefit Cost (Credit) Recognized in Expense (6.1) $ (7.6) $ (3.3)
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2020 7.5    
2021 7.7    
2022 8.0    
2023 8.2    
2024 8.4    
Years 2025 to 2029, in Total 40.6    
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2020 0.0    
2021 0.0    
2022 0.0    
2023 0.0    
2024 0.0    
Years 2025 to 2029, in Total $ 0.0