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Income Taxes (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Jun. 30, 2013
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   $ 6,101.1    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1],[2]                   (16.5)    
Federal:                        
Current                   (4.0) $ (30.7) $ 107.3
Deferred                   856.6 (28.8) 774.8
Total Federal                   901.2 (41.9) 882.1
State and Local:                        
Current                   16.0 (10.5) 14.5
Deferred                   44.9 (21.2) 23.0
Total State and Local                   68.5 (31.8) 37.5
Income Tax Expense (Credit)                   969.7 (73.7) 919.6
Income Tax Expense:                        
Deferred                   901.5 (50.0) 808.2
Income Tax Expense (Credit)                   969.7 (73.7) 919.6
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income $ 401.8 $ 556.7 $ 376.2 $ 594.2 $ 375.2 $ (764.2) [3] $ 503.9 $ 503.1   1,928.9 618.0 2,052.3
Discontinued Operations         0.0 0.0 2.5 [4] 0.0   0.0 2.5 (283.7)
Income Tax Expense (Credit)                   969.7 (73.7) 919.6
Pretax Income                   2,898.6 546.8 2,688.2
Income Taxes on Pretax Income at Statutory Rate (35%)                   1,014.5 191.4 940.9
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                   60.2 41.7 53.6
Investment Tax Credits, Net                   (18.8) (12.3) (11.6)
State and Local Income Taxes, Net                   54.7 (20.7) 24.4
Removal Costs                   (32.7) (39.8) (28.8)
AFUDC                   (37.4) (44.8) (51.6)
Valuation Allowance                   (1.8) (128.3) 17.2
U.K. Windfall Tax                   0.0 (12.9) 0.0
Tax Reform Adjustments                   (26.7) 0.0 0.0
Tax Adjustments                   (35.8) (43.9) (20.1)
Other                   (6.5) (4.1) (4.4)
Income Tax Expense (Credit)                   $ 969.7 $ (73.7) $ 919.6
Effective Income Tax Rate                   33.50% (13.50%) 34.20%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 3,504.6       2,753.0         $ 3,504.6 $ 2,753.0  
Deferred Tax Liabilities (10,318.5)       (14,637.4)         (10,318.5) (14,637.4)  
Property Related Temporary Differences (5,680.6)       (8,758.1)         (5,680.6) (8,758.1)  
Amounts Due from Customers for Future Federal Income Taxes 1,064.8       (292.2)         1,064.8 (292.2)  
Deferred State Income Taxes (1,124.4)       (976.6)         (1,124.4) (976.6)  
Securitized Assets (257.7)       (535.6)         (257.7) (535.6)  
Regulatory Assets (500.3)       (896.9)         (500.3) (896.9)  
Deferred Income Taxes on Other Comprehensive Loss 25.7       88.7         25.7 88.7  
Accrued Nuclear Decommissioning (457.0)       (666.8)         (457.0) (666.8)  
Net Operating Loss Carryforward 86.6       101.2         86.6 101.2  
Deferred Tax Assets, Tax Credit Carryforwards, General Business 174.7       45.1         174.7 45.1  
Investment in Partnership (222.0)       (349.6)         (222.0) (349.6)  
Valuation Allowance 0.0       (1.8)         0.0 (1.8) $ 130.0
All Other, Net 76.3       358.2         76.3 358.2  
Net Deferred Tax Liabilities (6,813.9)       (11,884.4)         (6,813.9) (11,884.4)  
Net Income Tax Operating Loss Carryforwards                        
Federal Net Income Tax Operating Loss                   230.1    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   1.7 2.7 2.7
Interest Income                   6.1 9.9 0.8
Reversal of Prior Period Interest Expense                   0.0 3.3 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 3.6       2.9         3.6 2.9  
Accrual for Payment of Interest and Penalties 8.3       5.8         8.3 5.8  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       98.8       187.0   98.8 187.0 182.0
Increase - Tax Positions Taken During a Prior Period                   4.5 86.0 5.4
Decrease - Tax Positions Taken During a Prior Period                   (28.0) (161.2) (0.4)
Increase - Tax Positions Taken During the Current Year                   3.4 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   7.9 (13.0) 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, 86.6       98.8         86.6 98.8 187.0
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount 10.5       15.8         $ 10.5 $ 15.8 $ 100.2
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Effect of Income Tax Reform on AEP's Other Business Operations                   $ 103.0    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1],[2]                   $ 16.5    
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ 969.7 $ (73.7) $ 919.6
Interest Income                   16.0 16.3 7.9
Net Income (Loss) 401.8 556.7 376.2 594.2 375.2 (764.2) [3] 503.9 503.1   $ 1,928.9 618.0 $ 2,052.3
Period with No Change in Unrecognized Tax Benefits                   12 months    
Original Indiana Corporate Income Tax Rate                   8.50%    
Reduction In Indiana Corporate Tax Rate                   0.50%    
Reduced Indiana Corporate Income Tax Rate                   6.50%    
Indiana Corporate Tax Rate                   4.90%    
Reduction In Income Tax New Rate                       6.50%
Pre-2016 TX Income/Franchise Tax Rate                   0.95%    
New TX Income/Franchise Tax Rate                   0.75%    
Anticipated TX Income/Franchise Tax Rate                   1.00%    
Valuation Allowance 0.0       (1.8)         $ 0.0 (1.8) $ 130.0
Transmission and Distribution Expenses Net Income Adjustment                     21.0  
Pre July 1 2017 Illinois Corporate Income Tax Rate                   5.25%    
Effective July 1 2017 Illinois Corporate Income Tax Rate                   7.00%    
Illinois Replacement Tax                   2.50%    
Pre July 1, 2017 Total Illinois Corporate Income Tax Rate                   7.75%    
Effective July 1, 2017 Total Illinois Corporate Income Tax Rate                   9.50%    
AEP Texas Inc. [Member]                        
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   $ 807.1    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1],[5]                   (117.4)    
Federal:                        
Current                   (85.7) 40.9 61.4
Deferred                   63.3 29.9 (7.1)
Total Federal                   (24.0) 69.1 52.6
State and Local:                        
Current                   0.6 (8.8) 5.6
Deferred                   0.0 (0.4) 0.0
Total State and Local                   0.6 (9.2) 5.6
Income Tax Expense (Credit)                   (23.4) 59.9 58.2
Income Tax Expense:                        
Deferred                   63.3 29.5 (7.1)
Income Tax Expense (Credit)                   (23.4) 59.9 58.2
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 163.9 64.3 49.0 33.3 55.8 8.1 49.0 33.7   310.5 146.6 120.3
Discontinued Operations         (0.6) [6] 47.4 [6] 0.7 [6] 1.3 [6]   0.0 48.8 1.4
Income Tax Expense (Credit)                   (23.4) 59.9 58.2
Pretax Income                   287.1 255.3 179.9
Income Taxes on Pretax Income at Statutory Rate (35%)                   100.5 89.4 63.0
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                   0.7 0.5 0.5
Investment Tax Credits, Net                   (1.6) (1.7) (1.7)
State and Local Income Taxes, Net                   0.4 (6.0) 3.6
Parent Company Loss Benefit                   0.0 (2.5) (3.1)
U.K. Windfall Tax                   0.0 (12.9) 0.0
Tax Reform Adjustments                   (117.4) 0.0 0.0
Tax Adjustments                   (4.2) (4.9) (1.6)
Other                   (1.8) (2.0) (2.5)
Income Tax Expense (Credit)                   $ (23.4) $ 59.9 $ 58.2
Effective Income Tax Rate                   (8.20%) 23.50% 32.40%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 221.0       135.8         $ 221.0 $ 135.8  
Deferred Tax Liabilities (1,134.1)       (1,667.5)         (1,134.1) (1,667.5)  
Property Related Temporary Differences (791.5)       (1,056.1)         (791.5) (1,056.1)  
Amounts Due from Customers for Future Federal Income Taxes 140.9       (5.7)         140.9 (5.7)  
Deferred State Income Taxes (27.5)       (24.2)         (27.5) (24.2)  
Securitized Assets (190.5)       (407.0)         (190.5) (407.0)  
Regulatory Assets (36.4)       (61.3)         (36.4) (61.3)  
Deferred Income Taxes on Other Comprehensive Loss 4.1       8.0         4.1 8.0  
Deferred Revenue 10.9       18.0         10.9 18.0  
All Other, Net (23.1)       (3.4)         (23.1) (3.4)  
Net Deferred Tax Liabilities (913.1)       (1,531.7)         (913.1) (1,531.7)  
Net Income Tax Operating Loss Carryforwards                        
Federal Net Income Tax Operating Loss                   261.8    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   0.0 0.0 $ 0.2
Interest Income                   1.1 0.2 0.2
Reversal of Prior Period Interest Expense                   0.0 0.8 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 2.8       2.1         2.8 2.1  
Accrual for Payment of Interest and Penalties 0.1       0.3         0.1 0.3  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       6.5       27.8   6.5 27.8 22.6
Increase - Tax Positions Taken During a Prior Period                   2.0 6.5 5.2
Decrease - Tax Positions Taken During a Prior Period                   (12.3) (15.0) 0.0
Increase - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   3.0 (12.8) 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, (0.8)       6.5         (0.8) 6.5 27.8
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount (0.5)       4.2         $ (0.5) 4.2 26.0
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1],[5]                   $ 117.4    
Discontinued Operations                     $ (27.5) $ (1.7)
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ (23.4) $ 59.9 $ 58.2
Net Income (Loss) 163.9 64.3 49.0 33.3 55.8 8.1 49.0 33.7   $ 310.5 146.6 120.3
Period with No Change in Unrecognized Tax Benefits                   12 months    
Transmission and Distribution Expenses Net Income Adjustment                     7.0  
AEP Transmission Co [Member]                        
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   $ 558.6    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   0.6    
Federal:                        
Current                   (127.5) (129.4) (126.3)
Deferred                   256.0 205.9 171.3
Total Federal                   128.5 76.5 45.0
State and Local:                        
Current                   1.9 0.4 3.1
Deferred                   16.8 17.2 11.9
Total State and Local                   18.7 17.6 15.0
Income Tax Expense (Credit)                   147.2 94.1 60.0
Income Tax Expense:                        
Deferred                   272.8 223.1 183.2
Income Tax Expense (Credit)                   147.2 94.1 60.0
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 61.8 59.9 107.4 57.0 39.7 52.4 74.8 25.8   286.1 192.7 132.9
Discontinued Operations         0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                   147.2 94.1 60.0
Pretax Income                   433.3 286.8 192.9
Income Taxes on Pretax Income at Statutory Rate (35%)                   151.7 100.4 67.5
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
State and Local Income Taxes, Net                   12.2 11.4 9.8
AFUDC                   (18.3) (18.3) (18.6)
Tax Reform Adjustments                   0.6 0.0 0.0
Other                   1.0 0.6 1.3
Income Tax Expense (Credit)                   $ 147.2 $ 94.1 $ 60.0
Effective Income Tax Rate                   34.00% 32.80% 31.10%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 162.7       61.4         $ 162.7 $ 61.4  
Deferred Tax Liabilities (764.4)       (923.5)         (764.4) (923.5)  
Property Related Temporary Differences (654.7)       (825.6)         (654.7) (825.6)  
Amounts Due from Customers for Future Federal Income Taxes 89.7       (37.2)         89.7 (37.2)  
Deferred State Income Taxes (77.4)       (55.6)         (77.4) (55.6)  
Deferred Federal Income Taxes on Deferred State Income Taxes 16.3       19.5         16.3 19.5  
Net Operating Loss Carryforward 16.8       33.3         16.8 33.3  
Deferred Tax Assets, Tax Credit Carryforwards, General Business 0.3       0.0         0.3 0.0  
Valuation Allowance 0.0       0.1         0.0 0.1  
All Other, Net 7.3       3.4         7.3 3.4  
Net Deferred Tax Liabilities (601.7)       (862.1)         (601.7) (862.1)  
Net Income Tax Operating Loss Carryforwards                        
Federal Net Income Tax Operating Loss                   344.1    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   0.0 0.0 $ 0.0
Interest Income                   0.0 0.0 0.0
Reversal of Prior Period Interest Expense                   0.0 0.0 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.0       0.0         0.0 0.0  
Accrual for Payment of Interest and Penalties 0.0       0.0         0.0 0.0  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       0.0       0.0   0.0 0.0 0.0
Increase - Tax Positions Taken During a Prior Period                   0.0 0.0 0.0
Decrease - Tax Positions Taken During a Prior Period                   0.0 0.0 0.0
Increase - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   0.0 0.0 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, 0.0       0.0         0.0 0.0 0.0
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount 0.0       0.0         $ 0.0 $ 0.0 $ 0.0
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   $ (0.6)    
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ 147.2 $ 94.1 $ 60.0
Net Income (Loss) 61.8 59.9 107.4 57.0 39.7 52.4 74.8 25.8   $ 286.1 192.7 $ 132.9
Period with No Change in Unrecognized Tax Benefits                   12 months    
Original Indiana Corporate Income Tax Rate                   8.50%    
Reduction In Indiana Corporate Tax Rate                   0.50%    
Reduced Indiana Corporate Income Tax Rate                   6.50%    
Indiana Corporate Tax Rate                   4.90%    
Reduction In Income Tax New Rate                       6.50%
Valuation Allowance 0.0       0.1         $ 0.0 0.1  
Appalachian Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   1,296.4    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   5.7    
Federal:                        
Current                   15.3 64.1  
Deferred                   166.9 125.8  
Deferred Investment Tax Credits                       $ (0.3)
Total Federal                   182.1 189.8  
State and Local:                        
Current                   (1.4) 4.4  
Deferred                   4.6 4.9  
Deferred Investment Tax Credits                       (0.3)
Total State and Local                   3.2 9.3  
Income Tax Expense (Credit)                   185.3 199.1 194.3
Income Tax Expense:                        
Current                       (32.9)
Deferred                   171.5 130.7 227.5
Deferred Investment Tax Credits                       (0.3)
Income Tax Expense (Credit)                   185.3 199.1 194.3
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 82.6 86.0 52.1 110.6 65.3 104.1 73.4 126.3   331.3 369.1 340.6
Discontinued Operations         0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                   185.3 199.1 194.3
Pretax Income                   516.6 568.2 534.9
Income Taxes on Pretax Income at Statutory Rate (35%)                   180.8 198.9 187.2
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                   18.0 19.3 19.8
Investment Tax Credits, Net                   (0.1) (0.1) (0.3)
State and Local Income Taxes, Net                   3.5 6.0 7.2
Removal Costs                   (12.4) (12.0) (9.9)
AFUDC                   (5.0) (6.1) (7.0)
Valuation Allowance                   0.0 (1.7) 1.7
Tax Reform Adjustments                   4.3 0.0 0.0
Other                   (3.8) (5.2) (4.4)
Income Tax Expense (Credit)                   $ 185.3 $ 199.1 $ 194.3
Effective Income Tax Rate                   35.90% 35.00% 36.30%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 614.4       413.5         $ 614.4 $ 413.5  
Deferred Tax Liabilities (2,180.1)       (3,085.8)         (2,180.1) (3,085.8)  
Property Related Temporary Differences (1,308.2)       (2,031.9)         (1,308.2) (2,031.9)  
Amounts Due from Customers for Future Federal Income Taxes 228.0       (73.1)         228.0 (73.1)  
Deferred State Income Taxes (335.7)       (319.3)         (335.7) (319.3)  
Securitized Assets (59.3)       (106.9)         (59.3) (106.9)  
Regulatory Assets (83.9)       (159.9)         (83.9) (159.9)  
Deferred Income Taxes on Other Comprehensive Loss (0.4)       4.5         (0.4) 4.5  
Deferred Tax Assets, Tax Credit Carryforwards, General Business 16.6       11.7         16.6 11.7  
All Other, Net (22.8)       2.6         (22.8) 2.6  
Net Deferred Tax Liabilities (1,565.7)       (2,672.3)         (1,565.7) (2,672.3)  
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   0.5 0.0 $ 0.4
Interest Income                   0.0 0.1 0.0
Reversal of Prior Period Interest Expense                   0.0 0.0 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.0       0.0         0.0 0.0  
Accrual for Payment of Interest and Penalties 1.0       0.1         1.0 0.1  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       0.0       0.3   0.0 0.3 0.0
Increase - Tax Positions Taken During a Prior Period                   0.0 0.0 0.3
Decrease - Tax Positions Taken During a Prior Period                   0.0 (0.3) 0.0
Increase - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   0.0 0.0 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, 0.0       0.0         0.0 0.0 0.3
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount 0.0       0.0         $ 0.0 $ 0.0 $ 0.2
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   $ (5.7)    
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ 185.3 $ 199.1 $ 194.3
Net Income (Loss) 82.6 86.0 52.1 110.6 65.3 104.1 73.4 126.3   $ 331.3 369.1 340.6
Period with No Change in Unrecognized Tax Benefits                   12 months    
Pre July 1 2017 Illinois Corporate Income Tax Rate                   5.25%    
Effective July 1 2017 Illinois Corporate Income Tax Rate                   7.00%    
Illinois Replacement Tax                   2.50%    
Pre July 1, 2017 Total Illinois Corporate Income Tax Rate                   7.75%    
Effective July 1, 2017 Total Illinois Corporate Income Tax Rate                   9.50%    
Indiana Michigan Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   $ 808.7    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   2.3    
Federal:                        
Current                   (106.5) (44.8)  
Deferred                   202.1 104.9  
Deferred Investment Tax Credits                       (3.3)
Total Federal                   90.9 63.9  
State and Local:                        
Current                   (8.1) 3.4  
Deferred                   (1.4) 0.2  
Deferred Investment Tax Credits                       (3.3)
Total State and Local                   (9.5) 3.6  
Income Tax Expense (Credit)                   81.4 67.5 96.1
Income Tax Expense:                        
Current                       5.2
Deferred                   200.7 105.1 94.2
Deferred Investment Tax Credits                       (3.3)
Income Tax Expense (Credit)                   81.4 67.5 96.1
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 42.9 64.9 10.5 68.4 38.5 75.4 51.3 74.7   186.7 239.9 204.8
Discontinued Operations         0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                   81.4 67.5 96.1
Pretax Income                   268.1 307.4 300.9
Income Taxes on Pretax Income at Statutory Rate (35%)                   93.8 107.6 105.3
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                   11.4 6.7 9.5
Investment Tax Credits, Net                   (4.7) (4.7) (3.3)
State and Local Income Taxes, Net                   (1.0) 2.4 5.8
Removal Costs                   (13.3) (21.3) (12.6)
AFUDC                   (5.6) (7.3) (6.2)
Tax Reform Adjustments                   (2.9) 0.0 0.0
Tax Adjustments                   2.7 (14.2) (4.2)
Other                   1.0 (1.7) 1.8
Income Tax Expense (Credit)                   $ 81.4 $ 67.5 $ 96.1
Effective Income Tax Rate                   30.40% 22.00% 31.90%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 1,096.4       912.9         $ 1,096.4 $ 912.9  
Deferred Tax Liabilities (2,050.2)       (2,440.3)         (2,050.2) (2,440.3)  
Property Related Temporary Differences (403.0)       (579.4)         (403.0) (579.4)  
Amounts Due from Customers for Future Federal Income Taxes 137.6       (50.4)         137.6 (50.4)  
Deferred State Income Taxes (180.6)       (158.7)         (180.6) (158.7)  
Regulatory Assets (43.8)       (81.0)         (43.8) (81.0)  
Deferred Income Taxes on Other Comprehensive Loss 3.9       8.8         3.9 8.8  
Accrued Nuclear Decommissioning (457.0)       (666.8)         (457.0) (666.8)  
Net Operating Loss Carryforward 1.6       7.1         1.6 7.1  
All Other, Net (12.5)       (7.0)         (12.5) (7.0)  
Net Deferred Tax Liabilities (953.8)       (1,527.4)         (953.8) (1,527.4)  
Net Income Tax Operating Loss Carryforwards                        
Federal Net Income Tax Operating Loss                   332.6    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   0.0 0.2 $ 0.2
Interest Income                   1.0 0.0 0.0
Reversal of Prior Period Interest Expense                   0.0 0.0 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.0       0.0         0.0 0.0  
Accrual for Payment of Interest and Penalties 1.3       0.9         1.3 0.9  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       3.8       2.4   3.8 2.4 2.3
Increase - Tax Positions Taken During a Prior Period                   0.2 1.8 0.1
Decrease - Tax Positions Taken During a Prior Period                   (0.5) (0.4) 0.0
Increase - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   (0.3) 0.0 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, 3.2       3.8         3.2 3.8 2.4
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount 2.1       2.5         $ 2.1 $ 2.5 $ 1.6
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   $ (2.3)    
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ 81.4 $ 67.5 $ 96.1
Net Income (Loss) 42.9 64.9 10.5 68.4 38.5 75.4 51.3 74.7   $ 186.7 239.9 $ 204.8
Period with No Change in Unrecognized Tax Benefits                   12 months    
Original Indiana Corporate Income Tax Rate                   8.50%    
Reduction In Indiana Corporate Tax Rate                   0.50%    
Reduced Indiana Corporate Income Tax Rate                   6.50%    
Indiana Corporate Tax Rate                   4.90%    
Reduction In Income Tax New Rate                       6.50%
Pre July 1 2017 Illinois Corporate Income Tax Rate                   5.25%    
Effective July 1 2017 Illinois Corporate Income Tax Rate                   7.00%    
Illinois Replacement Tax                   2.50%    
Pre July 1, 2017 Total Illinois Corporate Income Tax Rate                   7.75%    
Effective July 1, 2017 Total Illinois Corporate Income Tax Rate                   9.50%    
Ohio Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   $ 743.1    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1],[5]                   (14.3)    
Federal:                        
Current                   11.2 178.8  
Deferred                   141.3 (40.8)  
Deferred Investment Tax Credits                       $ (0.1)
Total Federal                   152.5 138.0  
State and Local:                        
Current                   0.2 4.2  
Deferred                   6.6 1.6  
Deferred Investment Tax Credits                       (0.1)
Total State and Local                   6.8 5.8  
Income Tax Expense (Credit)                   159.3 143.8 126.5
Income Tax Expense:                        
Current                       89.0
Deferred                   147.9 (39.2) 37.6
Deferred Investment Tax Credits                       (0.1)
Income Tax Expense (Credit)                   159.3 143.8 126.5
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 92.8 82.6 62.3 86.2 37.5 99.9 74.6 70.2   323.9 282.2 232.7
Discontinued Operations         0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                   159.3 143.8 126.5
Pretax Income                   483.2 426.0 359.2
Income Taxes on Pretax Income at Statutory Rate (35%)                   169.1 149.1 125.7
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                   7.6 7.1 8.2
Investment Tax Credits, Net                   0.0 0.0 (0.1)
State and Local Income Taxes, Net                   4.4 3.8 0.7
Tax Reform Adjustments                   (14.4) 0.0 0.0
Other                   (7.4) (16.2) (8.0)
Income Tax Expense (Credit)                   $ 159.3 $ 143.8 $ 126.5
Effective Income Tax Rate                   33.00% 33.80% 35.20%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 286.0       232.4         $ 286.0 $ 232.4  
Deferred Tax Liabilities (1,048.9)       (1,578.5)         (1,048.9) (1,578.5)  
Property Related Temporary Differences (761.2)       (1,090.8)         (761.2) (1,090.8)  
Amounts Due from Customers for Future Federal Income Taxes 127.3       (43.6)         127.3 (43.6)  
Deferred State Income Taxes (41.7)       (34.6)         (41.7) (34.6)  
Regulatory Assets (107.7)       (174.1)         (107.7) (174.1)  
Deferred Income Taxes on Other Comprehensive Loss (0.6)       (1.6)         (0.6) (1.6)  
Deferred Fuel and Purchased Power (24.5)       (117.6)         (24.5) (117.6)  
All Other, Net 45.5       116.2         45.5 116.2  
Net Deferred Tax Liabilities (762.9)       (1,346.1)         (762.9) (1,346.1)  
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   0.0 0.2 $ 1.0
Interest Income                   1.6 0.0 0.0
Reversal of Prior Period Interest Expense                   0.0 0.0 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.3       0.0         0.3 0.0  
Accrual for Payment of Interest and Penalties 1.0       1.7         1.0 1.7  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       6.9       6.9   6.9 6.9 6.9
Increase - Tax Positions Taken During a Prior Period                   0.0 0.0 0.0
Decrease - Tax Positions Taken During a Prior Period                   0.0 0.0 0.0
Increase - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   0.0 0.0 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, 6.9       6.9         6.9 6.9 6.9
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount 4.5       4.4         $ 4.5 $ 4.4 $ 4.5
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1],[5]                   $ 14.3    
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ 159.3 $ 143.8 $ 126.5
Net Income (Loss) 92.8 82.6 62.3 86.2 37.5 99.9 74.6 70.2   $ 323.9 282.2 232.7
Period with No Change in Unrecognized Tax Benefits                   12 months    
Pre July 1 2017 Illinois Corporate Income Tax Rate                   5.25%    
Effective July 1 2017 Illinois Corporate Income Tax Rate                   7.00%    
Illinois Replacement Tax                   2.50%    
Pre July 1, 2017 Total Illinois Corporate Income Tax Rate                   7.75%    
Effective July 1, 2017 Total Illinois Corporate Income Tax Rate                   9.50%    
Public Service Co Of Oklahoma [Member]                        
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   $ 538.6    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   2.8    
Federal:                        
Current                   (77.1) (28.0)  
Deferred                   122.7 77.2  
Deferred Investment Tax Credits                       (0.6)
Total Federal                   44.0 47.8  
State and Local:                        
Current                   (0.2) (1.9)  
Deferred                   2.0 5.3  
Deferred Investment Tax Credits                       (0.6)
Total State and Local                   6.1 6.6  
Income Tax Expense (Credit)                   50.1 54.4 51.3
Income Tax Expense:                        
Current                       (6.4)
Deferred                   124.7 82.5 58.3
Deferred Investment Tax Credits                       (0.6)
Income Tax Expense (Credit)                   50.1 54.4 51.3
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 0.6 46.2 20.4 4.8 2.6 52.8 28.9 15.7   72.0 100.0 92.5
Discontinued Operations         0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                   50.1 54.4 51.3
Pretax Income                   122.1 154.4 143.8
Income Taxes on Pretax Income at Statutory Rate (35%)                   42.7 54.0 50.3
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                   0.3 0.8 0.5
Investment Tax Credits, Net                   (1.6) (1.4) (1.8)
State and Local Income Taxes, Net                   4.0 4.2 5.1
AFUDC                   (0.2) (2.2) (3.1)
Tax Reform Adjustments                   2.8 0.0 0.0
Other                   2.1 (1.0) 0.3
Income Tax Expense (Credit)                   $ 50.1 $ 54.4 $ 51.3
Effective Income Tax Rate                   41.00% 35.20% 35.70%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 269.2       153.8         $ 269.2 $ 153.8  
Deferred Tax Liabilities (911.2)       (1,212.6)         (911.2) (1,212.6)  
Property Related Temporary Differences (623.8)       (927.3)         (623.8) (927.3)  
Amounts Due from Customers for Future Federal Income Taxes 111.6       (3.2)         111.6 (3.2)  
Deferred State Income Taxes (142.7)       (128.5)         (142.7) (128.5)  
Regulatory Assets (34.4)       (67.6)         (34.4) (67.6)  
Deferred Income Taxes on Other Comprehensive Loss (0.8)       (1.8)         (0.8) (1.8)  
Deferred Federal Income Taxes on Deferred State Income Taxes 33.5       50.6         33.5 50.6  
Net Operating Loss Carryforward 23.1       16.5         23.1 16.5  
Deferred Tax Assets, Tax Credit Carryforwards, General Business 0.7       0.0         0.7 0.0  
All Other, Net (9.2)       2.5         (9.2) 2.5  
Net Deferred Tax Liabilities (642.0)       (1,058.8)         (642.0) (1,058.8)  
Net Income Tax Operating Loss Carryforwards                        
Federal Net Income Tax Operating Loss                   213.9    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   0.0 0.0 $ 0.1
Interest Income                   0.0 0.3 0.0
Reversal of Prior Period Interest Expense                   0.0 0.7 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.6       0.6         0.6 0.6  
Accrual for Payment of Interest and Penalties 0.0       0.0         0.0 0.0  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       0.1       1.3   0.1 1.3 1.3
Increase - Tax Positions Taken During a Prior Period                   0.1 0.1 0.0
Decrease - Tax Positions Taken During a Prior Period                   (0.9) (1.3) 0.0
Increase - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   0.7 0.0 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, 0.0       0.1         0.0 0.1 1.3
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount 0.0       0.1         $ 0.0 $ 0.1 $ 0.9
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   $ (2.8)    
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ 50.1 $ 54.4 $ 51.3
Net Income (Loss) 0.6 46.2 20.4 4.8 2.6 52.8 28.9 15.7   $ 72.0 100.0 92.5
Period with No Change in Unrecognized Tax Benefits                   12 months    
Pre-2016 TX Income/Franchise Tax Rate                   0.95%    
New TX Income/Franchise Tax Rate                   0.75%    
Anticipated TX Income/Franchise Tax Rate                   1.00%    
Transmission and Distribution Expenses Net Income Adjustment                     2.0  
Southwestern Electric Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Decrease in Deferred Income Tax Liabilities                   $ 782.9    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   0.7    
Federal:                        
Current                   (30.1) (96.7)  
Deferred                   84.8 172.6  
Deferred Investment Tax Credits                       (1.4)
Total Federal                   53.3 74.7  
State and Local:                        
Current                   (0.9) (12.6)  
Deferred                   (4.3) (10.0)  
Deferred Investment Tax Credits                       (1.4)
Total State and Local                   (5.2) (22.6)  
Income Tax Expense (Credit)                   48.1 52.1 84.8
Income Tax Expense:                        
Current                       44.3
Deferred                   80.5 162.6 41.9
Deferred Investment Tax Credits                       (1.4)
Income Tax Expense (Credit)                   48.1 52.1 84.8
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 11.0 84.1 25.1 17.3 16.5 84.4 44.3 24.5   137.5 169.7 196.0
Discontinued Operations         0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                   48.1 52.1 84.8
Pretax Income                   185.6 221.8 280.8
Income Taxes on Pretax Income at Statutory Rate (35%)                   65.0 77.6 98.3
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                   1.9 3.2 3.1
Depletion                   (5.7) (5.5) (5.5)
Investment Tax Credits, Net                   (1.4) (1.2) (1.4)
State and Local Income Taxes, Net                   (2.3) (14.7) 4.8
AFUDC                   (0.9) (3.9) (9.2)
Tax Reform Adjustments                   (0.4) 0.0 0.0
Tax Adjustments                   (9.9) (0.9) (3.9)
Other                   1.8 (2.5) (1.4)
Income Tax Expense (Credit)                   $ 48.1 $ 52.1 $ 84.8
Effective Income Tax Rate                   25.90% 23.50% 30.20%
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 349.4       230.5         $ 349.4 $ 230.5  
Deferred Tax Liabilities (1,267.1)       (1,837.4)         (1,267.1) (1,837.4)  
Property Related Temporary Differences (908.8)       (1,445.2)         (908.8) (1,445.2)  
Amounts Due from Customers for Future Federal Income Taxes 135.8       (48.2)         135.8 (48.2)  
Deferred State Income Taxes (189.2)       (175.1)         (189.2) (175.1)  
Regulatory Assets (30.8)       (40.7)         (30.8) (40.7)  
Deferred Income Taxes on Other Comprehensive Loss 1.3       5.1         1.3 5.1  
Impairment Loss 17.4       20.3         17.4 20.3  
Net Operating Loss Carryforward 38.7       40.3         38.7 40.3  
Deferred Tax Assets, Tax Credit Carryforwards, General Business 0.8       0.1         0.8 0.1  
All Other, Net 17.1       36.5         17.1 36.5  
Net Deferred Tax Liabilities (917.7)       (1,606.9)         (917.7) (1,606.9)  
Net Income Tax Operating Loss Carryforwards                        
Federal Net Income Tax Operating Loss                   87.6    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                   0.0 0.0 $ 0.4
Interest Income                   0.0 0.0 0.0
Reversal of Prior Period Interest Expense                   0.0 1.4 0.0
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.0       0.1         0.0 0.1  
Accrual for Payment of Interest and Penalties 0.0       0.0         0.0 0.0  
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       1.3       9.3   1.3 9.3 7.5
Increase - Tax Positions Taken During a Prior Period                   1.7 1.3 1.8
Decrease - Tax Positions Taken During a Prior Period                   (5.4) (9.3) 0.0
Increase - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Tax Positions Taken During the Current Year                   0.0 0.0 0.0
Decrease - Settlements with Taxing Authorities                   1.6 0.0 0.0
Decrease - Lapse of the Applicable Statute of Limitations                   0.0 0.0 0.0
Balance at December 31, (0.8)       1.3         (0.8) 1.3 9.3
Tax Contingency [Abstract]                        
Unrecognized Tax Benefits, if Recognized - Amount (0.5)       0.8         $ (0.5) $ 0.8 $ 6.0
Income Taxes (Textuals) [Abstract]                        
Future Statutory Tax Rate on Pretax Income                   21.00%    
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform [1]                   $ (0.7)    
Statutory Tax Rate on Pretax Income                   35.00% 35.00% 35.00%
Limit on Utiliization of Net Operating Losses Arising After December 31, 2017                   80.00%    
Income Tax Expense (Credit)                   $ 48.1 $ 52.1 $ 84.8
Net Income (Loss) 11.0 $ 84.1 $ 25.1 $ 17.3 16.5 $ 84.4 $ 44.3 $ 24.5   $ 137.5 169.7 196.0
Period with No Change in Unrecognized Tax Benefits                   12 months    
Pre-2016 TX Income/Franchise Tax Rate                   0.95%    
New TX Income/Franchise Tax Rate                   0.75%    
Anticipated TX Income/Franchise Tax Rate                   1.00%    
Transmission and Distribution Expenses Net Income Adjustment                     9.0  
AEP Transmission Holdco's Equity Investment in ETT [Member]                        
Income Taxes (Textuals) [Abstract]                        
Excess Accumulated Deferred Income Taxes                   $ 154.0    
Arkansas [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 72.0                 $ 72.0    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2022    
Arkansas [Member] | Southwestern Electric Power Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 71.2                 $ 71.2    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2022    
Kentucky [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 157.6                 $ 157.6    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
Louisiana [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 543.1                 $ 543.1    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
Louisiana [Member] | Southwestern Electric Power Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 533.4                 $ 533.4    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
Oklahoma [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 799.8                 $ 799.8    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
Oklahoma [Member] | AEP Transmission Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 296.9                 $ 296.9    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
Oklahoma [Member] | Public Service Co Of Oklahoma [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 477.0                 $ 477.0    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
Tennessee [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 27.9                 $ 27.9    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2032    
Virginia [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 17.8                 $ 17.8    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
West Virginia [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 29.2                 $ 29.2    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
West Virginia [Member] | Indiana Michigan Power Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 14.1                 $ 14.1    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2037    
Ohio Municipal [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 106.3                 $ 106.3    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2022    
Ohio Municipal [Member] | AEP Transmission Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 64.2                 $ 64.2    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2022    
Federal [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ 48.6 17.6 0.0
State and Local:                        
Deferred Investment Tax Credits                   48.6 17.6 0.0
Income Tax Expense:                        
Deferred Investment Tax Credits                   48.6 17.6 0.0
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 4.0                 $ 4.0    
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2036    
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 174.7                 $ 174.7    
Tax Credit Carryforward Amount To Expire If Not Used 145.8                 145.8    
Income Taxes (Textuals) [Abstract]                        
Uncertain Tax Positions Netted Against Tax Credit and Alternative Minimum Tax Carryforward Tax Benefits 0.0       17.0         $ 0.0 17.0  
Federal [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Federal [Member] | AEP Texas Inc. [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ (1.6) (1.7) (1.7)
State and Local:                        
Deferred Investment Tax Credits                   (1.6) (1.7) (1.7)
Income Tax Expense:                        
Deferred Investment Tax Credits                   (1.6) (1.7) (1.7)
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.6                 0.6    
Tax Credit Carryforward Amount To Expire If Not Used 0.3                 $ 0.3    
Federal [Member] | AEP Texas Inc. [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | AEP Texas Inc. [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Federal [Member] | AEP Transmission Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ 0.0 0.0 0.0
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0 0.0
Income Tax Expense:                        
Deferred Investment Tax Credits                   $ 0.0 0.0 $ 0.0
Net Income Tax Operating Loss Carryforwards                        
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2036    
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.3                 $ 0.3    
Tax Credit Carryforward Amount To Expire If Not Used 0.1                 $ 0.1    
Federal [Member] | AEP Transmission Co [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | AEP Transmission Co [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Federal [Member] | Appalachian Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ (0.1) (0.1)  
State and Local:                        
Deferred Investment Tax Credits                   (0.1) (0.1)  
Income Tax Expense:                        
Deferred Investment Tax Credits                   (0.1) (0.1)  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 16.6                 16.6    
Tax Credit Carryforward Amount To Expire If Not Used 6.1                 $ 6.1    
Federal [Member] | Appalachian Power Co [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | Appalachian Power Co [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Federal [Member] | Indiana Michigan Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ (4.7) 3.8  
State and Local:                        
Deferred Investment Tax Credits                   (4.7) 3.8  
Income Tax Expense:                        
Deferred Investment Tax Credits                   $ (4.7) 3.8  
Net Income Tax Operating Loss Carryforwards                        
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2036    
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 10.6                 $ 10.6    
Tax Credit Carryforward Amount To Expire If Not Used 10.1                 $ 10.1    
Federal [Member] | Indiana Michigan Power Co [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | Indiana Michigan Power Co [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Federal [Member] | Ohio Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ 0.0 0.0  
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0  
Income Tax Expense:                        
Deferred Investment Tax Credits                   0.0 0.0  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 14.8                 14.8    
Tax Credit Carryforward Amount To Expire If Not Used 1.0                 $ 1.0    
Federal [Member] | Ohio Power Co [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | Ohio Power Co [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Federal [Member] | Public Service Co Of Oklahoma [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ (1.6) (1.4)  
State and Local:                        
Deferred Investment Tax Credits                   (1.6) (1.4)  
Income Tax Expense:                        
Deferred Investment Tax Credits                   $ (1.6) (1.4)  
Net Income Tax Operating Loss Carryforwards                        
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2036    
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.7                 $ 0.7    
Tax Credit Carryforward Amount To Expire If Not Used 0.7                 $ 0.7    
Federal [Member] | Public Service Co Of Oklahoma [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | Public Service Co Of Oklahoma [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Federal [Member] | Southwestern Electric Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                   $ (1.4) (1.2)  
State and Local:                        
Deferred Investment Tax Credits                   (1.4) (1.2)  
Income Tax Expense:                        
Deferred Investment Tax Credits                   $ (1.4) $ (1.2)  
Net Income Tax Operating Loss Carryforwards                        
Operating Loss Carryforwards, Expiration Date                   Dec. 31, 2036    
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.8                 $ 0.8    
Tax Credit Carryforward Amount To Expire If Not Used 0.7                 $ 0.7    
Federal [Member] | Southwestern Electric Power Co [Member] | Maximum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Dec. 31, 2036    
Federal [Member] | Southwestern Electric Power Co [Member] | Minimum [Member]                        
Income Taxes (Textuals) [Abstract]                        
Tax Credit Carryforward, Expiration Date                   Jan. 01, 2032    
Uk Windfall Tax Issue [Member]                        
State and Local:                        
Income Tax Expense (Credit)                 $ 80.0      
Income Tax Expense:                        
Income Tax Expense (Credit)                 80.0      
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Income Tax Expense (Credit)                 80.0      
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Income Tax Expense (Credit)                 80.0      
Income Taxes (Textuals) [Abstract]                        
Income Tax Expense (Credit)                 80.0      
Interest Income                 $ 43.0      
Tax Increase Prevention Act of 2014 [Member] | Appalachian Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                       50.00%
Tax Increase Prevention Act of 2014 [Member] | Indiana Michigan Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                       50.00%
Tax Increase Prevention Act of 2014 [Member] | Ohio Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                       50.00%
Tax Increase Prevention Act of 2014 [Member] | Public Service Co Of Oklahoma [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                       50.00%
Tax Increase Prevention Act of 2014 [Member] | Southwestern Electric Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                       50.00%
Protecting Americans from Tax Hikes Act of 2015 [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Protecting Americans from Tax Hikes Act of 2015 [Member] | AEP Texas Inc. [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Protecting Americans from Tax Hikes Act of 2015 [Member] | AEP Transmission Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Protecting Americans from Tax Hikes Act of 2015 [Member] | Appalachian Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Protecting Americans from Tax Hikes Act of 2015 [Member] | Indiana Michigan Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Protecting Americans from Tax Hikes Act of 2015 [Member] | Ohio Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Protecting Americans from Tax Hikes Act of 2015 [Member] | Public Service Co Of Oklahoma [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Protecting Americans from Tax Hikes Act of 2015 [Member] | Southwestern Electric Power Co [Member]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
Bonus Depreciation Extension Phase Down 40                     40.00%  
Bonus Depreciation Extension Phase Down 30                     30.00%  
Solar Investment Tax Credit                     30.00%  
Net Tax Benefit [Member]                        
Income Taxes (Textuals) [Abstract]                        
Discontinued Operations                   $ 0.0 $ 0.0 $ 6.2
Net Tax Benefit [Member] | AEP Texas Inc. [Member]                        
Income Taxes (Textuals) [Abstract]                        
Discontinued Operations                   0.0 27.6 1.8
Expiration of Charitable Contribution Carryforward Deductions [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance         6.0           6.0 17.0
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance         6.0           6.0 17.0
Investment in Operations of AEPRO [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance                       156.0
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance                       156.0
Sale of AEPRO [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance                       48.0
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance                       $ 48.0
2011 Audit Issue Settlement [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance         56.0           56.0  
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance         56.0           56.0  
Certain Assets Held for Sale and 2015 Federal Income Tax Return [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance         66.0           66.0  
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance         $ 66.0           66.0  
Reversal of Unrealized Capital Loss Carryforward [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance 2.0                 2.0    
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance 2.0                 2.0    
Federal Tax Reform [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets [2]                   470.2    
Increase (Decrease) in Regulatory Liabilities [2]                   5,614.4    
Federal Tax Reform [Member] | AEP Texas Inc. [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets                   12.1    
Increase (Decrease) in Regulatory Liabilities                   677.6    
Federal Tax Reform [Member] | AEP Transmission Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets                   66.9    
Increase (Decrease) in Regulatory Liabilities                   492.3    
Federal Tax Reform [Member] | Appalachian Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets                   129.1    
Increase (Decrease) in Regulatory Liabilities                   1,173.0    
Federal Tax Reform [Member] | Indiana Michigan Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets                   85.3    
Increase (Decrease) in Regulatory Liabilities                   725.7    
Federal Tax Reform [Member] | Ohio Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets                   62.7    
Increase (Decrease) in Regulatory Liabilities                   666.1    
Federal Tax Reform [Member] | Public Service Co Of Oklahoma [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets                   8.3    
Increase (Decrease) in Regulatory Liabilities                   533.1    
Federal Tax Reform [Member] | Southwestern Electric Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase (Decrease) in Other Regulatory Assets                   69.8    
Increase (Decrease) in Regulatory Liabilities                   713.8    
Deregulated Generation Assets and Deferred Fuel [Member] | AEP Texas Inc. [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (113.0)    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   113.0    
Deregulated Generation Assets and Deferred Fuel [Member] | Ohio Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (16.0)    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   16.0    
Net Regulatory Liability for Tax Reform [Member]                        
Income Taxes (Textuals) [Abstract]                        
Excess Accumulated Deferred Income Taxes                   4,400.0    
Incremental Liability for Tax Reform [Member]                        
Income Taxes (Textuals) [Abstract]                        
Excess Accumulated Deferred Income Taxes                   1,200.0    
Pretax Excess ADIT [Member]                        
Income Taxes (Textuals) [Abstract]                        
Excess Accumulated Deferred Income Taxes                   4,400.0    
Temporary Differences Associated with Depreciable Property [Member]                        
Income Taxes (Textuals) [Abstract]                        
Excess Accumulated Deferred Income Taxes                   3,200.0    
Remaining Excess ADIT [Member]                        
Income Taxes (Textuals) [Abstract]                        
Excess Accumulated Deferred Income Taxes                   1,200.0    
State and Local Jurisdiction [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   7.6 (0.1)  
State and Local:                        
Deferred Investment Tax Credits                   7.6 (0.1)  
Income Tax Expense:                        
Deferred Investment Tax Credits                   7.6 (0.1)  
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance 5.0                 5.0    
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 31.0                 31.0    
Tax Credit Carryforward Amount To Expire If Not Used 31.0                 31.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   10.0    
Valuation Allowance 5.0                 5.0    
State and Local Jurisdiction [Member] | AEP Texas Inc. [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   0.0 0.0  
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0  
Income Tax Expense:                        
Deferred Investment Tax Credits                   0.0 0.0  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.0                 0.0    
Tax Credit Carryforward Amount To Expire If Not Used 0.0                 0.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   10.0    
State and Local Jurisdiction [Member] | AEP Transmission Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   0.0 0.0  
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0  
Income Tax Expense:                        
Deferred Investment Tax Credits                   0.0 0.0  
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance 2.0                 2.0    
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.0                 0.0    
Tax Credit Carryforward Amount To Expire If Not Used 0.0                 0.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   10.0    
Valuation Allowance 2.0                 2.0    
State and Local Jurisdiction [Member] | Appalachian Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   0.0 0.0  
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0  
Income Tax Expense:                        
Deferred Investment Tax Credits                   0.0 0.0  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.0                 0.0    
Tax Credit Carryforward Amount To Expire If Not Used 0.0                 0.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   10.0    
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   0.0 0.0  
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0  
Income Tax Expense:                        
Deferred Investment Tax Credits                   0.0 0.0  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.0                 0.0    
Tax Credit Carryforward Amount To Expire If Not Used 0.0                 0.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   10.0    
State and Local Jurisdiction [Member] | Ohio Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   0.0 0.0  
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0  
Income Tax Expense:                        
Deferred Investment Tax Credits                   0.0 0.0  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.0                 0.0    
Tax Credit Carryforward Amount To Expire If Not Used 0.0                 0.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   10.0    
State and Local Jurisdiction [Member] | Public Service Co Of Oklahoma [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   4.3 3.2  
State and Local:                        
Deferred Investment Tax Credits                   4.3 3.2  
Income Tax Expense:                        
Deferred Investment Tax Credits                   4.3 3.2  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 31.0                 31.0    
Tax Credit Carryforward Amount To Expire If Not Used 31.0                 31.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   10.0    
State and Local Jurisdiction [Member] | Southwestern Electric Power Co [Member]                        
Federal Tax Reform [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   (10.0)    
Federal:                        
Deferred Investment Tax Credits                   0.0 0.0  
State and Local:                        
Deferred Investment Tax Credits                   0.0 0.0  
Income Tax Expense:                        
Deferred Investment Tax Credits                   0.0 $ 0.0  
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.0                 0.0    
Tax Credit Carryforward Amount To Expire If Not Used $ 0.0                 0.0    
Income Taxes (Textuals) [Abstract]                        
Increase(Decrease) in Income Tax Expense (Benefit) from Tax Reform                   $ 10.0    
[1] In 2017, in contemplation of corporate federal tax reform, the Registrants adopted a method under Internal Revenue Section 162 for deducting repair and maintenance costs associated with transmission and distribution property. This change resulted in a decrease in state income tax expense of approximately $10 million that has been excluded from the tables above.
[2] The effect of Tax Reform on AEP’s other business operations (other than the Registrant Subsidiaries), which primarily include unregulated activities in the Generation & Marketing segment, transmission operations reflected in the AEP Transmission Holdco segment and activities recorded in Corporate and Other, increased income tax expense for the year-ended December 31, 2017 by approximately $103 million.
[3] Includes impairments for certain merchant generation assets (see Note 7).
[4] Includes final accounting adjustment for sale of AEPRO (see Note 7).
[5] AEP Texas and OPCo recorded favorable adjustments to income tax expense of approximately $113 million and $16 million related to previously owned deregulated generation assets and certain deferred fuel amounts, respectively.
[6] Includes the transfer of the Wind Farms (see Note 7).