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Benefit Plans 3 (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 72.9 $ 73.6 $ 70.5
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 Plan Surcharge   10.00% 5.00%
Multiemployer Plans Withdrawal Obligation $ 39.0 $ 31.0  
Noncurrent Regulatory Assets 5,625.5 5,140.3  
UMWA Withdrawal Obligation [Member]      
Benefit Plans Textuals [Abstract]      
Noncurrent Regulatory Assets 20.0 14.0  
Appalachian Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 7.3 $ 7.2 $ 7.3
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 Plan Surcharge 10.00% 5.00%  
Noncurrent Regulatory Assets $ 1,121.1 $ 1,154.2  
Indiana Michigan Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 10.9 10.6 10.5
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 $ 916.6 804.3  
Ohio Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 5.6 5.4 5.2
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 $ 1,107.5 1,113.0  
Public Service Co Of Oklahoma [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 4.3 4.2 4.0
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 $ 340.2 214.8  
Southwestern Electric Power Co [Member]      
American Electric Power System Retirement Savings Plans      
Cost of Company Matching Contributions $ 5.7 5.7 5.3
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 $ 551.2 415.8  
Pension Plans [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 4,915.8 4,832.7  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 5,085.8 4,992.9 5,224.9
Accumulated Benefit Obligation 4,915.8 4,832.7  
Fair Value of Plan Assets 4,827.3 4,767.6 4,967.5
Underfunded Status, Accumulated Benefit Obligation (88.5) (65.1)  
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 98.2    
Components of Net Periodic Benefit Cost      
Service Cost 85.8 93.5 71.9
Interest Cost 211.6 205.3 221.0
Expected Return on Plan Assets (280.3) (274.8) (261.6)
Amortization of Prior Service Cost (Credit) 2.3 2.2 2.5
Amortization of Net Actuarial Loss 83.8 107.1 124.0
Net Periodic Benefit Cost (Credit) 103.2 133.3 157.8
Capitalized Portion (37.8) (48.4) (52.2)
Net Periodic Benefit Cost (Credit) Recognized in Expense 65.4 84.9 105.6
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 84.2    
Prior Service Cost (Credit) 1.0    
Total Estimated 2017 Amortization 85.2    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 85.2    
Pension Plans [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 332.6    
2018 335.6    
2019 344.5    
2020 351.2    
2021 364.4    
Years 2022 to 2026, in Total 1,841.2    
Pension Plans [Member] | Appalachian Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 641.3 641.9  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 654.0 653.4 702.8
Accumulated Benefit Obligation 641.3 641.9  
Fair Value of Plan Assets 606.4 603.2 642.3
Underfunded Status, Accumulated Benefit Obligation (34.9) (38.7)  
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 10.2    
Components of Net Periodic Benefit Cost      
Service Cost 8.1 8.7 7.0
Interest Cost 27.2 26.7 29.6
Expected Return on Plan Assets (35.3) (35.0) (33.9)
Amortization of Prior Service Cost (Credit) 0.1 0.2 0.2
Amortization of Net Actuarial Loss 10.8 13.9 16.6
Net Periodic Benefit Cost (Credit) 10.9 14.5 19.5
Capitalized Portion (4.1) (5.5) (6.8)
Net Periodic Benefit Cost (Credit) Recognized in Expense 6.8 9.0 12.7
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 10.7    
Prior Service Cost (Credit) 0.2    
Total Estimated 2017 Amortization 10.9    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 10.9    
Pension Plans [Member] | Appalachian Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 43.2    
2018 42.9    
2019 43.8    
2020 44.5    
2021 46.0    
Years 2022 to 2026, in Total 231.2    
Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 588.8 571.7  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 611.6 591.5 617.9
Accumulated Benefit Obligation 588.8 571.7  
Fair Value of Plan Assets 586.1 570.0 591.7
Underfunded Status, Accumulated Benefit Obligation (2.7) (1.7)  
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 13.6    
Components of Net Periodic Benefit Cost      
Service Cost 12.2 12.9 10.0
Interest Cost 25.3 24.5 26.3
Expected Return on Plan Assets (33.6) (32.6) (31.0)
Amortization of Prior Service Cost (Credit) 0.1 0.2 0.2
Amortization of Net Actuarial Loss 10.0 12.6 14.6
Net Periodic Benefit Cost (Credit) 14.0 17.6 20.1
Capitalized Portion (3.3) (4.0) (4.6)
Net Periodic Benefit Cost (Credit) Recognized in Expense 10.7 13.6 15.5
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 10.0    
Prior Service Cost (Credit) 0.2    
Total Estimated 2017 Amortization 10.2    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 10.2    
Pension Plans [Member] | Indiana Michigan Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 35.7    
2018 35.9    
2019 38.6    
2020 38.7    
2021 40.2    
Years 2022 to 2026, in Total 216.5    
Pension Plans [Member] | Ohio Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 478.0 484.2  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 492.9 497.5 526.3
Accumulated Benefit Obligation 478.0 484.2  
Fair Value of Plan Assets 473.8 472.1 498.5
Underfunded Status, Accumulated Benefit Obligation (4.2) (12.1)  
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 7.6    
Components of Net Periodic Benefit Cost      
Service Cost 6.5 6.7 5.2
Interest Cost 20.6 20.3 22.1
Expected Return on Plan Assets (27.6) (27.5) (26.5)
Amortization of Prior Service Cost (Credit) 0.1 0.2 0.2
Amortization of Net Actuarial Loss 8.1 10.5 12.4
Net Periodic Benefit Cost (Credit) 7.7 10.2 13.4
Capitalized Portion (3.4) (4.8) (5.5)
Net Periodic Benefit Cost (Credit) Recognized in Expense 4.3 5.4 7.9
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 8.1    
Prior Service Cost (Credit) 0.1    
Total Estimated 2017 Amortization 8.2    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 8.2    
Pension Plans [Member] | Ohio Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 35.8    
2018 35.7    
2019 35.8    
2020 36.1    
2021 35.4    
Years 2022 to 2026, in Total 172.6    
Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 254.2 254.4  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 266.7 265.4 285.4
Accumulated Benefit Obligation 254.2 254.4  
Fair Value of Plan Assets 266.0 262.1 275.5
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 5.5    
Components of Net Periodic Benefit Cost      
Service Cost 6.2 6.4 5.2
Interest Cost 11.2 10.9 12.1
Expected Return on Plan Assets (15.5) (15.1) (14.6)
Amortization of Prior Service Cost (Credit) 0.3 0.2 0.3
Amortization of Net Actuarial Loss 4.4 5.7 6.7
Net Periodic Benefit Cost (Credit) 6.6 8.1 9.7
Capitalized Portion (2.4) (2.8) (3.3)
Net Periodic Benefit Cost (Credit) Recognized in Expense 4.2 5.3 6.4
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 4.4    
Prior Service Cost (Credit) 0.0    
Total Estimated 2017 Amortization 4.4    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 4.4    
Pension Plans [Member] | Public Service Co Of Oklahoma [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 19.6    
2018 19.3    
2019 20.3    
2020 20.4    
2021 21.9    
Years 2022 to 2026, in Total 106.7    
Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 281.5 269.3  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 296.6 282.8 298.2
Accumulated Benefit Obligation 281.5 269.3  
Fair Value of Plan Assets 287.3 280.6 290.2
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 8.7    
Components of Net Periodic Benefit Cost      
Service Cost 8.1 8.3 6.6
Interest Cost 12.4 11.8 12.7
Expected Return on Plan Assets (16.4) (16.0) (15.4)
Amortization of Prior Service Cost (Credit) 0.3 0.3 0.3
Amortization of Net Actuarial Loss 4.8 6.0 7.1
Net Periodic Benefit Cost (Credit) 9.2 10.4 11.3
Capitalized Portion (2.7) (3.2) (3.4)
Net Periodic Benefit Cost (Credit) Recognized in Expense 6.5 7.2 7.9
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 4.9    
Prior Service Cost (Credit) 0.0    
Total Estimated 2017 Amortization 4.9    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 4.9    
Pension Plans [Member] | Southwestern Electric Power Co [Member] | Pension Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 20.1    
2018 21.3    
2019 22.0    
2020 22.6    
2021 23.6    
Years 2022 to 2026, in Total 122.2    
Qualified Pension Plans [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 4,846.0 4,757.1  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 4,846.0 4,757.1  
Qualified Pension Plans [Member] | Appalachian Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 641.0 641.4  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 641.0 641.4  
Qualified Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 588.5 571.3  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 588.5 571.3  
Qualified Pension Plans [Member] | Ohio Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 478.0 484.1  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 478.0 484.1  
Qualified Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 252.0 252.0  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 252.0 252.0  
Qualified Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 279.8 267.7  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 279.8 267.7  
Nonqualified Pension Plans [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 69.8 75.6  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 69.8 75.6  
Nonqualified Pension Plans [Member] | Appalachian Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.3 0.5  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.3 0.5  
Nonqualified Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.3 0.4  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.3 0.4  
Nonqualified Pension Plans [Member] | Ohio Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.0 0.1  
Underfunded Accumulated Benefit Obligation      
Accumulated Benefit Obligation 0.0 0.1  
Nonqualified Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 2.2 2.4  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 2.3 2.6  
Accumulated Benefit Obligation 2.2 2.4  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Accumulated Benefit Obligation (2.2) (2.4)  
Nonqualified Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Accumulated Benefit Obligation      
Accumulated Benefit Obligation 1.7 1.6  
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 1.7 1.7  
Accumulated Benefit Obligation 1.7 1.6  
Fair Value of Plan Assets 0.0 0.0  
Underfunded Status, Accumulated Benefit Obligation (1.7) (1.6)  
Other Postretirement Benefit Plans [Member]      
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 1,447.4 1,450.6 1,439.0
Fair Value of Plan Assets 1,545.9 1,577.4 1,693.9
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 4.3    
Components of Net Periodic Benefit Cost      
Service Cost 10.2 12.2 14.2
Interest Cost 60.9 56.8 67.2
Expected Return on Plan Assets (107.0) (111.0) (111.3)
Amortization of Prior Service Cost (Credit) (69.0) (69.1) (69.0)
Amortization of Net Actuarial Loss 31.4 18.8 22.1
Net Periodic Benefit Cost (Credit) (73.5) (92.3) (76.8)
Capitalized Portion 26.9 33.5 25.3
Net Periodic Benefit Cost (Credit) Recognized in Expense (46.6) (58.8) (51.5)
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 34.4    
Prior Service Cost (Credit) (69.0)    
Total Estimated 2017 Amortization (34.6)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (34.6)    
Other Postretirement Benefit Plans [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 137.0    
2018 138.2    
2019 138.3    
2020 139.7    
2021 141.1    
Years 2022 to 2026, in Total 718.0    
Other Postretirement Benefit Plans [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2017 0.3    
2018 0.3    
2019 0.3    
2020 0.3    
2021 0.3    
Years 2022 to 2026, in Total 1.7    
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 255.6 262.2 267.1
Fair Value of Plan Assets 246.9 256.7 280.6
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 2.4    
Components of Net Periodic Benefit Cost      
Service Cost 1.0 1.1 1.4
Interest Cost 10.8 10.3 12.8
Expected Return on Plan Assets (17.3) (18.1) (18.5)
Amortization of Prior Service Cost (Credit) (10.1) (10.0) (10.1)
Amortization of Net Actuarial Loss 5.4 3.6 4.6
Net Periodic Benefit Cost (Credit) (10.2) (13.1) (9.8)
Capitalized Portion 3.9 5.0 3.4
Net Periodic Benefit Cost (Credit) Recognized in Expense (6.3) (8.1) (6.4)
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 5.8    
Prior Service Cost (Credit) (10.0)    
Total Estimated 2017 Amortization (4.2)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (4.2)    
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 25.4    
2018 25.6    
2019 25.2    
2020 25.2    
2021 25.1    
Years 2022 to 2026, in Total 122.7    
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2017 0.2    
2018 0.2    
2019 0.2    
2020 0.2    
2021 0.2    
Years 2022 to 2026, in Total 1.0    
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 167.6 166.3 161.7
Fair Value of Plan Assets 186.6 189.0 202.4
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 1.5 1.6 1.9
Interest Cost 7.0 6.4 7.6
Expected Return on Plan Assets (12.9) (13.2) (13.4)
Amortization of Prior Service Cost (Credit) (9.4) (9.4) (9.4)
Amortization of Net Actuarial Loss 3.7 2.0 2.4
Net Periodic Benefit Cost (Credit) (10.1) (12.6) (10.9)
Capitalized Portion 2.4 2.9 2.5
Net Periodic Benefit Cost (Credit) Recognized in Expense (7.7) (9.7) (8.4)
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 4.1    
Prior Service Cost (Credit) (9.4)    
Total Estimated 2017 Amortization (5.3)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (5.3)    
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 16.6    
2018 16.7    
2019 16.8    
2020 16.9    
2021 17.2    
Years 2022 to 2026, in Total 87.6    
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2017 0.0    
2018 0.0    
2019 0.0    
2020 0.0    
2021 0.0    
Years 2022 to 2026, in Total 0.0    
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 164.0 168.6 164.7
Fair Value of Plan Assets 182.6 191.6 206.2
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 0.8 0.9 1.0
Interest Cost 7.0 6.4 7.6
Expected Return on Plan Assets (13.0) (13.4) (13.5)
Amortization of Prior Service Cost (Credit) (6.9) (7.0) (6.9)
Amortization of Net Actuarial Loss 3.8 2.1 2.4
Net Periodic Benefit Cost (Credit) (8.3) (11.0) (9.4)
Capitalized Portion 3.7 5.2 3.8
Net Periodic Benefit Cost (Credit) Recognized in Expense (4.6) (5.8) (5.6)
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 4.0    
Prior Service Cost (Credit) (6.9)    
Total Estimated 2017 Amortization (2.9)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (2.9)    
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 17.0    
2018 17.0    
2019 17.0    
2020 16.9    
2021 16.9    
Years 2022 to 2026, in Total 83.8    
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2017 0.0    
2018 0.0    
2019 0.0    
2020 0.0    
2021 0.0    
Years 2022 to 2026, in Total 0.0    
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 77.6 77.7 76.7
Fair Value of Plan Assets 86.4 88.3 96.0
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 0.6 0.7 0.8
Interest Cost 3.3 3.0 3.6
Expected Return on Plan Assets (6.1) (6.3) (6.3)
Amortization of Prior Service Cost (Credit) (4.3) (4.3) (4.3)
Amortization of Net Actuarial Loss 1.8 1.0 1.1
Net Periodic Benefit Cost (Credit) (4.7) (5.9) (5.1)
Capitalized Portion 1.7 2.0 1.7
Net Periodic Benefit Cost (Credit) Recognized in Expense (3.0) (3.9) (3.4)
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 1.9    
Prior Service Cost (Credit) (4.3)    
Total Estimated 2017 Amortization (2.4)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (2.4)    
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 7.6    
2018 7.6    
2019 7.7    
2020 7.9    
2021 7.9    
Years 2022 to 2026, in Total 41.1    
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2017 0.0    
2018 0.0    
2019 0.0    
2020 0.0    
2021 0.0    
Years 2022 to 2026, in Total 0.0    
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Underfunded Accumulated Benefit Obligation      
Projected Benefit Obligation 86.9 86.1 85.0
Fair Value of Plan Assets 96.8 97.8 106.4
Estimated Future Benefit Payments and Contributions      
Expected Contributions and Payments During 2017 0.0    
Components of Net Periodic Benefit Cost      
Service Cost 0.8 0.8 1.0
Interest Cost 3.6 3.4 4.0
Expected Return on Plan Assets (6.8) (6.9) (7.0)
Amortization of Prior Service Cost (Credit) (5.0) (5.2) (5.2)
Amortization of Net Actuarial Loss 1.9 1.1 1.2
Net Periodic Benefit Cost (Credit) (5.5) (6.8) (6.0)
Capitalized Portion 1.6 2.1 1.8
Net Periodic Benefit Cost (Credit) Recognized in Expense (3.9) $ (4.7) $ (4.2)
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Net Actuarial Loss 2.2    
Prior Service Cost (Credit) (5.2)    
Total Estimated 2017 Amortization (3.0)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (3.0)    
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member] | Benefit Payments [Member]      
Estimated Future Benefit Payments and Contributions      
2017 8.0    
2018 8.1    
2019 8.2    
2020 8.4    
2021 8.7    
Years 2022 to 2026, in Total 46.6    
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member] | Medicare Subsidy Receipts [Member]      
Estimated Future Benefit Payments and Contributions      
2017 0.0    
2018 0.0    
2019 0.0    
2020 0.0    
2021 0.0    
Years 2022 to 2026, in Total 0.0    
Regulatory Assets [Member] | Pension Plans [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 74.1    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 74.1    
Regulatory Assets [Member] | Pension Plans [Member] | Appalachian Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 10.9    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 10.9    
Regulatory Assets [Member] | Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 9.6    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 9.6    
Regulatory Assets [Member] | Pension Plans [Member] | Ohio Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 8.2    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 8.2    
Regulatory Assets [Member] | Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 4.4    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 4.4    
Regulatory Assets [Member] | Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 4.9    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 4.9    
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (25.1)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (25.1)    
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (2.2)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (2.2)    
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (4.8)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (4.8)    
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (2.9)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (2.9)    
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (2.4)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (2.4)    
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (1.9)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (1.9)    
Deferred Income Taxes [Member] | Pension Plans [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 3.9    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 3.9    
Deferred Income Taxes [Member] | Pension Plans [Member] | Appalachian Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Deferred Income Taxes [Member] | Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.2    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.2    
Deferred Income Taxes [Member] | Pension Plans [Member] | Ohio Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Deferred Income Taxes [Member] | Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Deferred Income Taxes [Member] | Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (3.3)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (3.3)    
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (0.7)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (0.7)    
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (0.2)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (0.2)    
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (0.4)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (0.4)    
Net of Tax AOCI [Member] | Pension Plans [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 7.2    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 7.2    
Net of Tax AOCI [Member] | Pension Plans [Member] | Appalachian Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Net of Tax AOCI [Member] | Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.4    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.4    
Net of Tax AOCI [Member] | Pension Plans [Member] | Ohio Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Net of Tax AOCI [Member] | Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Net of Tax AOCI [Member] | Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (6.2)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (6.2)    
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (1.3)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (1.3)    
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (0.3)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 (0.3)    
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization 0.0    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 0.0    
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs      
Total Estimated 2017 Amortization (0.7)    
Expected to be Recorded as      
Estimated Amounts Expected to be Amortized to Net Periodic Benefit Costs in 2017 $ (0.7)