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Benefit Plans 1 (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs $ 2,106.6 $ 2,131.3  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability (890.6) (895.8)  
Appalachian Power Co [Member]      
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 113.7 137.6  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability (57.7) (54.2)  
Indiana Michigan Power Co [Member]      
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 140.9 129.4  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability (119.4) (162.2)  
Ohio Power Co [Member]      
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 259.6 253.9  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability (30.7) (25.5)  
Public Service Co Of Oklahoma [Member]      
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 6.4 3.3  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability (13.7) (13.6)  
Southwestern Electric Power Co [Member]      
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 75.8 78.7  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability $ (49.3) $ (47.3)  
Pension Plans [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Rate of Compensation Increase [1] 4.80% 4.80%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.00% 6.00% 6.50%
Rate of Compensation Increase [2] 4.80% 4.85% 4.95%
Change in Benefit Obligation      
Benefit Obligation as of January 1 $ 5,224.9 $ 4,841.7  
Service Cost 93.5 71.9 $ 69.2
Interest Cost 205.3 221.0 202.8
Actuarial (Gain) Loss (200.6) 387.0  
Benefit Payments (330.2) (296.7)  
Participant Contributions 0.0 0.0  
Medicare Subsidy 0.0 0.0  
Benefit Obligation as of December 31 4,992.9 5,224.9 4,841.7
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 4,967.5 4,711.2  
Actual Gain (Loss) on Plan Assets 32.4 474.2  
Company Contributions 97.9 78.8  
Participant Contributions 0.0 0.0  
Benefit Payments (330.2) (296.7)  
Fair Value of Plan Assets as of December 31 4,767.6 4,967.5 $ 4,711.2
Funded (Underfunded) Status as of December 31 (225.3) (257.4)  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 0.0 0.0  
Other Current Liabilities - Accrued Short-term Benefit Liability (6.3) (6.2)  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability (219.0) (251.2)  
Funded (Underfunded) Status (225.3) (257.4)  
Components      
Net Actuarial Loss 1,546.1 1,611.4  
Prior Service Cost (Credit) 3.3 5.5  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 41.8 174.4  
Amortization of Actuarial Gain (Loss) (107.1) (124.0)  
Amortization of Prior Service Credit (Cost) (2.2) (2.5)  
Change for the Year $ (67.5) $ 47.9  
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase [1] 4.80% 4.80%  
Pension Plans [Member] | Appalachian Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Rate of Compensation Increase [1] 4.45% 4.45%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.00% 6.00% 6.50%
Rate of Compensation Increase [2] 4.45% 4.60% 4.70%
Change in Benefit Obligation      
Benefit Obligation as of January 1 $ 702.8 $ 663.2  
Service Cost 8.7 7.0 $ 6.2
Interest Cost 26.7 29.6 27.7
Actuarial (Gain) Loss (41.4) 41.7  
Benefit Payments (43.4) (38.7)  
Participant Contributions 0.0 0.0  
Medicare Subsidy 0.0 0.0  
Benefit Obligation as of December 31 653.4 702.8 663.2
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 642.3 628.0  
Actual Gain (Loss) on Plan Assets (5.7) 44.0  
Company Contributions 10.0 9.0  
Participant Contributions 0.0 0.0  
Benefit Payments (43.4) (38.7)  
Fair Value of Plan Assets as of December 31 603.2 642.3 $ 628.0
Funded (Underfunded) Status as of December 31 (50.2) (60.5)  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 0.0 0.0  
Other Current Liabilities - Accrued Short-term Benefit Liability 0.0 0.0  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability (50.2) (60.5)  
Funded (Underfunded) Status (50.2) (60.5)  
Components      
Net Actuarial Loss 220.8 235.0  
Prior Service Cost (Credit) 0.3 0.5  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year (0.3) 31.6  
Amortization of Actuarial Gain (Loss) (13.9) (16.6)  
Amortization of Prior Service Credit (Cost) (0.2) (0.2)  
Change for the Year $ (14.4) $ 14.8  
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase [1] 4.45% 4.45%  
Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Rate of Compensation Increase [1] 4.75% 4.80%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.00% 6.00% 6.50%
Rate of Compensation Increase [2] 4.80% 4.90% 5.00%
Change in Benefit Obligation      
Benefit Obligation as of January 1 $ 617.9 $ 574.7  
Service Cost 12.9 10.0 $ 8.7
Interest Cost 24.5 26.3 24.1
Actuarial (Gain) Loss (28.4) 38.5  
Benefit Payments (35.4) (31.6)  
Participant Contributions 0.0 0.0  
Medicare Subsidy 0.0 0.0  
Benefit Obligation as of December 31 591.5 617.9 574.7
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 591.7 559.1  
Actual Gain (Loss) on Plan Assets (0.9) 55.3  
Company Contributions 14.6 8.9  
Participant Contributions 0.0 0.0  
Benefit Payments (35.4) (31.6)  
Fair Value of Plan Assets as of December 31 570.0 591.7 $ 559.1
Funded (Underfunded) Status as of December 31 (21.5) (26.2)  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 0.0 0.0  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability (21.5) (26.2)  
Funded (Underfunded) Status (21.5) (26.2)  
Components      
Net Actuarial Loss 130.0 137.9  
Prior Service Cost (Credit) 0.3 0.5  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 4.7 14.2  
Amortization of Actuarial Gain (Loss) (12.6) (14.6)  
Amortization of Prior Service Credit (Cost) (0.2) (0.2)  
Change for the Year $ (8.1) $ (0.6)  
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase [1] 4.75% 4.80%  
Pension Plans [Member] | Ohio Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Rate of Compensation Increase [1] 4.85% 4.80%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.00% 6.00% 6.50%
Rate of Compensation Increase [2] 4.80% 5.00% 5.00%
Change in Benefit Obligation      
Benefit Obligation as of January 1 $ 526.3 $ 523.6  
Service Cost 6.7 5.2 $ 5.3
Interest Cost 20.3 22.1 21.9
Actuarial (Gain) Loss (19.5) 6.8  
Benefit Payments (36.3) (31.4)  
Participant Contributions 0.0 0.0  
Medicare Subsidy 0.0 0.0  
Benefit Obligation as of December 31 497.5 526.3 523.6
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 498.5 501.6  
Actual Gain (Loss) on Plan Assets 2.2 21.7  
Company Contributions 7.7 6.6  
Participant Contributions 0.0 0.0  
Benefit Payments (36.3) (31.4)  
Fair Value of Plan Assets as of December 31 472.1 498.5 $ 501.6
Funded (Underfunded) Status as of December 31 (25.4) (27.8)  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 0.0 0.0  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability (25.4) (27.8)  
Funded (Underfunded) Status (25.4) (27.8)  
Components      
Net Actuarial Loss 222.0 226.7  
Prior Service Cost (Credit) 0.2 0.4  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 5.8 11.5  
Amortization of Actuarial Gain (Loss) (10.5) (12.4)  
Amortization of Prior Service Credit (Cost) (0.2) (0.2)  
Change for the Year $ (4.9) $ (1.1)  
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase [1] 4.85% 4.80%  
Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Rate of Compensation Increase [1] 4.85% 4.80%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.00% 6.00% 6.50%
Rate of Compensation Increase [2] 4.80% 4.90% 4.90%
Change in Benefit Obligation      
Benefit Obligation as of January 1 $ 285.4 $ 260.7  
Service Cost 6.4 5.2 $ 5.6
Interest Cost 10.9 12.1 11.0
Actuarial (Gain) Loss (17.9) 25.7  
Benefit Payments (19.4) (18.3)  
Participant Contributions 0.0 0.0  
Medicare Subsidy 0.0 0.0  
Benefit Obligation as of December 31 265.4 285.4 260.7
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 275.5 264.6  
Actual Gain (Loss) on Plan Assets 0.1 24.6  
Company Contributions 5.9 4.6  
Participant Contributions 0.0 0.0  
Benefit Payments (19.4) (18.3)  
Fair Value of Plan Assets as of December 31 262.1 275.5 $ 264.6
Funded (Underfunded) Status as of December 31 (3.3) (9.9)  
Benefit Amounts Recognized on the Balance Sheets      
Employee Benefits and Pension Assets - Prepaid Benefit Costs 0.0 0.0  
Other Current Liabilities - Accrued Short-term Benefit Liability (0.2) (0.2)  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability (3.1) (9.7)  
Funded (Underfunded) Status (3.3) (9.9)  
Components      
Net Actuarial Loss 94.1 102.7  
Prior Service Cost (Credit) 0.3 0.5  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year (2.9) 15.7  
Amortization of Actuarial Gain (Loss) (5.7) (6.7)  
Amortization of Prior Service Credit (Cost) (0.2) (0.3)  
Change for the Year $ (8.8) $ 8.7  
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase [1] 4.85% 4.80%  
Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Rate of Compensation Increase [1] 4.80% 4.80%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.00% 6.00% 6.50%
Rate of Compensation Increase [2] 4.80% 4.85% 4.75%
Change in Benefit Obligation      
Benefit Obligation as of January 1 $ 298.2 $ 270.6  
Service Cost 8.3 6.6 $ 7.0
Interest Cost 11.8 12.7 11.5
Actuarial (Gain) Loss (16.2) 27.5  
Benefit Payments (19.3) (19.2)  
Participant Contributions 0.0 0.0  
Medicare Subsidy 0.0 0.0  
Benefit Obligation as of December 31 282.8 298.2 270.6
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 290.2 279.0  
Actual Gain (Loss) on Plan Assets 1.6 26.5  
Company Contributions 8.1 3.9  
Participant Contributions 0.0 0.0  
Benefit Payments (19.3) (19.2)  
Fair Value of Plan Assets as of December 31 280.6 290.2 $ 279.0
Funded (Underfunded) Status as of December 31 (2.2) (8.0)  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 0.0 0.0  
Other Current Liabilities - Accrued Short-term Benefit Liability (0.1) (0.1)  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability (2.1) (7.9)  
Funded (Underfunded) Status (2.2) (8.0)  
Components      
Net Actuarial Loss 97.1 104.9  
Prior Service Cost (Credit) 0.4 0.7  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year (1.8) 16.5  
Amortization of Actuarial Gain (Loss) (6.0) (7.1)  
Amortization of Prior Service Credit (Cost) (0.3) (0.3)  
Change for the Year $ (8.1) $ 9.1  
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase [1] 4.80% 4.80%  
Pension Plans [Member] | Minimum [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 3.50%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 3.50%    
Pension Plans [Member] | Minimum [Member] | Appalachian Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 3.50%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 3.50%    
Pension Plans [Member] | Minimum [Member] | Indiana Michigan Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 3.50%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 3.50%    
Pension Plans [Member] | Minimum [Member] | Ohio Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 3.50%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 3.50%    
Pension Plans [Member] | Minimum [Member] | Public Service Co Of Oklahoma [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 3.50%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 3.50%    
Pension Plans [Member] | Minimum [Member] | Southwestern Electric Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 3.50%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 3.50%    
Pension Plans [Member] | Maximum [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 12.00%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 12.00%    
Pension Plans [Member] | Maximum [Member] | Appalachian Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 12.00%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 12.00%    
Pension Plans [Member] | Maximum [Member] | Indiana Michigan Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 12.00%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 12.00%    
Pension Plans [Member] | Maximum [Member] | Ohio Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 12.00%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 12.00%    
Pension Plans [Member] | Maximum [Member] | Public Service Co Of Oklahoma [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 12.00%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 12.00%    
Pension Plans [Member] | Maximum [Member] | Southwestern Electric Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Rate of Compensation Increase 12.00%    
Benefit Plans (Textuals) [Abstract]      
Rate of Compensation Increase 12.00%    
Other Postretirement Benefit Plans [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.75% 6.75% 7.00%
Health Care Trend Rates      
Initial 6.25% 6.50%  
Ultimate 5.00% 5.00%  
Year Ultimate Reached 2020 2020  
Effect of a 1% Change in Assumed Health Care Cost Trend Rates for the OPEB Health Care Plans      
Effect of 1% Increase on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost $ 3.7    
Effect of 1% Decrease on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost (3.0)    
Effect of 1% Increase on the Health Care Component of the Accumulated Postretirement Benefit Obligation 70.5    
Effect of 1% Decrease on the Health Care Component of the Accumulated Postretirement Benefit Obligation (57.4)    
Change in Benefit Obligation      
Benefit Obligation as of January 1 1,439.0 $ 1,455.5  
Service Cost 12.2 14.2 $ 22.9
Interest Cost 56.8 67.2 70.8
Actuarial (Gain) Loss 37.2 (14.4)  
Benefit Payments (128.7) (133.7)  
Participant Contributions 33.3 41.9  
Medicare Subsidy 0.8 8.3  
Benefit Obligation as of December 31 1,450.6 1,439.0 1,455.5
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 1,693.9 1,698.7  
Actual Gain (Loss) on Plan Assets (34.0) 82.7  
Company Contributions 12.9 4.3  
Participant Contributions 33.3 41.9  
Benefit Payments (128.7) (133.7)  
Fair Value of Plan Assets as of December 31 1,577.4 1,693.9 $ 1,698.7
Funded (Underfunded) Status as of December 31 126.8 254.9  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 185.8 336.7  
Other Current Liabilities - Accrued Short-term Benefit Liability (3.3) (3.6)  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability (55.7) (78.2)  
Funded (Underfunded) Status 126.8 254.9  
Components      
Net Actuarial Loss 577.4 419.9  
Prior Service Cost (Credit) (554.4) (623.5)  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 176.3 14.0  
Amortization of Actuarial Gain (Loss) (18.8) (22.1)  
Amortization of Prior Service Credit (Cost) 69.1 69.0  
Change for the Year $ 226.6 $ 60.9  
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.75% 6.75% 7.00%
Health Care Trend Rates      
Initial 6.25% 6.50%  
Ultimate 5.00% 5.00%  
Year Ultimate Reached 2020 2020  
Effect of a 1% Change in Assumed Health Care Cost Trend Rates for the OPEB Health Care Plans      
Effect of 1% Increase on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost $ 0.8    
Effect of 1% Decrease on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost (0.6)    
Effect of 1% Increase on the Health Care Component of the Accumulated Postretirement Benefit Obligation 15.2    
Effect of 1% Decrease on the Health Care Component of the Accumulated Postretirement Benefit Obligation (12.3)    
Change in Benefit Obligation      
Benefit Obligation as of January 1 267.1 $ 279.9  
Service Cost 1.1 1.4 $ 2.6
Interest Cost 10.3 12.8 13.5
Actuarial (Gain) Loss 2.5 (9.0)  
Benefit Payments (24.7) (26.6)  
Participant Contributions 5.7 7.2  
Medicare Subsidy 0.2 1.4  
Benefit Obligation as of December 31 262.2 267.1 279.9
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 280.6 284.8  
Actual Gain (Loss) on Plan Assets (7.7) 11.8  
Company Contributions 2.8 3.4  
Participant Contributions 5.7 7.2  
Benefit Payments (24.7) (26.6)  
Fair Value of Plan Assets as of December 31 256.7 280.6 $ 284.8
Funded (Underfunded) Status as of December 31 (5.5) 13.5  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 30.8 56.5  
Other Current Liabilities - Accrued Short-term Benefit Liability (2.6) (2.9)  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability (33.7) (40.1)  
Funded (Underfunded) Status (5.5) 13.5  
Components      
Net Actuarial Loss 86.9 65.8  
Prior Service Cost (Credit) (80.6) (90.6)  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 24.7 (2.3)  
Amortization of Actuarial Gain (Loss) (3.6) (4.6)  
Amortization of Prior Service Credit (Cost) 10.0 10.1  
Change for the Year $ 31.1 $ 3.2  
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.75% 6.75% 7.00%
Health Care Trend Rates      
Initial 6.25% 6.50%  
Ultimate 5.00% 5.00%  
Year Ultimate Reached 2020 2020  
Effect of a 1% Change in Assumed Health Care Cost Trend Rates for the OPEB Health Care Plans      
Effect of 1% Increase on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost $ 0.3    
Effect of 1% Decrease on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost (0.3)    
Effect of 1% Increase on the Health Care Component of the Accumulated Postretirement Benefit Obligation 6.8    
Effect of 1% Decrease on the Health Care Component of the Accumulated Postretirement Benefit Obligation (5.6)    
Change in Benefit Obligation      
Benefit Obligation as of January 1 161.7 $ 166.5  
Service Cost 1.6 1.9 $ 3.2
Interest Cost 6.4 7.6 8.2
Actuarial (Gain) Loss 7.7 (4.9)  
Benefit Payments (15.2) (15.7)  
Participant Contributions 4.0 5.2  
Medicare Subsidy 0.1 1.1  
Benefit Obligation as of December 31 166.3 161.7 166.5
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 202.4 206.2  
Actual Gain (Loss) on Plan Assets (2.3) 6.6  
Company Contributions 0.1 0.1  
Participant Contributions 4.0 5.2  
Benefit Payments (15.2) (15.7)  
Fair Value of Plan Assets as of December 31 189.0 202.4 $ 206.2
Funded (Underfunded) Status as of December 31 22.7 40.7  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 22.7 40.7  
Deferred Credits and Other Noncurrent Liabilities - Accrued Long-term Benefit Liability 0.0 0.0  
Funded (Underfunded) Status 22.7 40.7  
Components      
Net Actuarial Loss 77.1 54.4  
Prior Service Cost (Credit) (75.7) (85.1)  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 24.7 1.9  
Amortization of Actuarial Gain (Loss) (2.0) (2.4)  
Amortization of Prior Service Credit (Cost) 9.4 9.4  
Change for the Year $ 32.1 $ 8.9  
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.75% 6.75% 7.00%
Health Care Trend Rates      
Initial 6.25% 6.50%  
Ultimate 5.00% 5.00%  
Year Ultimate Reached 2020 2020  
Effect of a 1% Change in Assumed Health Care Cost Trend Rates for the OPEB Health Care Plans      
Effect of 1% Increase on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost $ 0.3    
Effect of 1% Decrease on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost (0.2)    
Effect of 1% Increase on the Health Care Component of the Accumulated Postretirement Benefit Obligation 6.9    
Effect of 1% Decrease on the Health Care Component of the Accumulated Postretirement Benefit Obligation (5.7)    
Change in Benefit Obligation      
Benefit Obligation as of January 1 164.7 $ 171.2  
Service Cost 0.9 1.0 $ 2.9
Interest Cost 6.4 7.6 9.5
Actuarial (Gain) Loss 8.7 (4.3)  
Benefit Payments (16.3) (17.4)  
Participant Contributions 4.3 5.6  
Medicare Subsidy (0.1) 1.0  
Benefit Obligation as of December 31 168.6 164.7 171.2
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 206.2 212.0  
Actual Gain (Loss) on Plan Assets (2.6) 6.0  
Company Contributions 0.0 0.0  
Participant Contributions 4.3 5.6  
Benefit Payments (16.3) (17.4)  
Fair Value of Plan Assets as of December 31 191.6 206.2 $ 212.0
Funded (Underfunded) Status as of December 31 23.0 41.5  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 23.0 41.5  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability 0.0 0.0  
Funded (Underfunded) Status 23.0 41.5  
Components      
Net Actuarial Loss 52.6 30.7  
Prior Service Cost (Credit) (55.4) (62.4)  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 24.0 3.3  
Amortization of Actuarial Gain (Loss) (2.1) (2.4)  
Amortization of Prior Service Credit (Cost) 7.0 6.9  
Change for the Year $ 28.9 $ 7.8  
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.75% 6.75% 7.00%
Health Care Trend Rates      
Initial 6.25% 6.50%  
Ultimate 5.00% 5.00%  
Year Ultimate Reached 2020 2020  
Effect of a 1% Change in Assumed Health Care Cost Trend Rates for the OPEB Health Care Plans      
Effect of 1% Increase on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost $ 0.1    
Effect of 1% Decrease on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost (0.1)    
Effect of 1% Increase on the Health Care Component of the Accumulated Postretirement Benefit Obligation 3.2    
Effect of 1% Decrease on the Health Care Component of the Accumulated Postretirement Benefit Obligation (2.6)    
Change in Benefit Obligation      
Benefit Obligation as of January 1 76.7 $ 77.8  
Service Cost 0.7 0.8 $ 1.4
Interest Cost 3.0 3.6 3.8
Actuarial (Gain) Loss 2.4 (1.0)  
Benefit Payments (7.1) (7.3)  
Participant Contributions 1.9 2.3  
Medicare Subsidy 0.1 0.5  
Benefit Obligation as of December 31 77.7 76.7 77.8
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 96.0 96.3  
Actual Gain (Loss) on Plan Assets (2.5) 4.7  
Company Contributions 0.0 0.0  
Participant Contributions 1.9 2.3  
Benefit Payments (7.1) (7.3)  
Fair Value of Plan Assets as of December 31 88.3 96.0 $ 96.3
Funded (Underfunded) Status as of December 31 10.6 19.3  
Benefit Amounts Recognized on the Balance Sheets      
Employee Benefits and Pension Assets - Prepaid Benefit Costs 10.6 19.3  
Other Current Liabilities - Accrued Short-term Benefit Liability 0.0 0.0  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability 0.0 0.0  
Funded (Underfunded) Status 10.6 19.3  
Components      
Net Actuarial Loss 35.2 25.3  
Prior Service Cost (Credit) (34.5) (38.8)  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 10.9 0.6  
Amortization of Actuarial Gain (Loss) (1.0) (1.1)  
Amortization of Prior Service Credit (Cost) 4.3 4.3  
Change for the Year $ 14.2 $ 3.8  
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Actuarial Assumptions for Benefit Obligations      
Discount Rate 4.30% 4.00%  
Actuarial Assumptions for Net Periodic Benefit Costs      
Discount Rate 4.00% 4.70% 3.95%
Expected Return on Plan Assets 6.75% 6.75% 7.00%
Health Care Trend Rates      
Initial 6.25% 6.50%  
Ultimate 5.00% 5.00%  
Year Ultimate Reached 2020 2020  
Effect of a 1% Change in Assumed Health Care Cost Trend Rates for the OPEB Health Care Plans      
Effect of 1% Increase on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost $ 0.2    
Effect of 1% Decrease on Total Service and Interest Cost Components of Net Periodic Postretirement Health Care Benefit Cost (0.1)    
Effect of 1% Increase on the Health Care Component of the Accumulated Postretirement Benefit Obligation 3.5    
Effect of 1% Decrease on the Health Care Component of the Accumulated Postretirement Benefit Obligation (2.9)    
Change in Benefit Obligation      
Benefit Obligation as of January 1 85.0 $ 87.0  
Service Cost 0.8 1.0 $ 1.7
Interest Cost 3.4 4.0 4.3
Actuarial (Gain) Loss 2.1 (2.3)  
Benefit Payments (7.4) (7.7)  
Participant Contributions 2.1 2.5  
Medicare Subsidy 0.1 0.5  
Benefit Obligation as of December 31 86.1 85.0 87.0
Change in Fair Value of Plan Assets      
Fair Value of Plan Assets as of January 1 106.4 107.7  
Actual Gain (Loss) on Plan Assets (3.3) 3.9  
Company Contributions 0.0 0.0  
Participant Contributions 2.1 2.5  
Benefit Payments (7.4) (7.7)  
Fair Value of Plan Assets as of December 31 97.8 106.4 $ 107.7
Funded (Underfunded) Status as of December 31 11.7 21.4  
Benefit Amounts Recognized on the Balance Sheets      
Deferred Charges and Other Noncurrent Assets - Prepaid Benefit Costs 11.7 21.4  
Other Current Liabilities - Accrued Short-term Benefit Liability 0.0 0.0  
Employee Benefits and Pension Obligations - Accrued Long-term Benefit Liability 0.0 0.0  
Funded (Underfunded) Status 11.7 21.4  
Components      
Net Actuarial Loss 43.3 32.4  
Prior Service Cost (Credit) (41.6) (46.8)  
Components of Change in Amounts Included in AOCI and Regulatory Assets      
Actuarial (Gain) Loss During the Year 12.0 0.8  
Amortization of Actuarial Gain (Loss) (1.1) (1.2)  
Amortization of Prior Service Credit (Cost) 5.2 5.2  
Change for the Year 16.1 4.8  
Regulatory Assets [Member] | Pension Plans [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 1,385.2 1,418.3  
Regulatory Assets [Member] | Pension Plans [Member] | Appalachian Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 218.3 232.8  
Regulatory Assets [Member] | Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 125.3 134.1  
Regulatory Assets [Member] | Pension Plans [Member] | Ohio Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 222.2 227.1  
Regulatory Assets [Member] | Pension Plans [Member] | Public Service Co Of Oklahoma [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 94.4 103.2  
Regulatory Assets [Member] | Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 97.5 105.6  
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 15.1 (148.5)  
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets (0.7) (20.3)  
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 1.1 (26.3)  
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets (2.8) (31.7)  
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 0.7 (13.5)  
Regulatory Assets [Member] | Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 1.2 (8.9)  
Deferred Income Taxes [Member] | Pension Plans [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 57.5 69.5  
Deferred Income Taxes [Member] | Pension Plans [Member] | Appalachian Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 1.0 0.9  
Deferred Income Taxes [Member] | Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 1.8 1.5  
Deferred Income Taxes [Member] | Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 0.0 0.0  
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 2.8 (19.3)  
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 2.4 (1.6)  
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 0.1 (1.5)  
Deferred Income Taxes [Member] | Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 0.2 (1.9)  
Net of Tax AOCI [Member] | Pension Plans [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 106.7 129.1  
Net of Tax AOCI [Member] | Pension Plans [Member] | Appalachian Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 1.8 1.8  
Net of Tax AOCI [Member] | Pension Plans [Member] | Indiana Michigan Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 3.2 2.8  
Net of Tax AOCI [Member] | Pension Plans [Member] | Southwestern Electric Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 0.0 0.0  
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 5.1 (35.8)  
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 4.6 (2.9)  
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets 0.2 (2.9)  
Net of Tax AOCI [Member] | Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Recorded as      
Total of Amounts Included in AOCI and Regulatory Assets $ 0.3 $ (3.6)  
[1] Rates are for base pay only. In addition, an amount is added to reflect target incentive compensation for exempt employees and overtime and incentive pay for nonexempt employees.
[2] Rates are for base pay only. In addition, an amount is added to reflect target incentive compensation for exempt employees and overtime and incentive pay for nonexempt employees.