XML 1132 R71.htm IDEA: XBRL DOCUMENT v3.6.0.2
Income Taxes (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Federal:                        
Current                 $ (30.7) $ 107.3 $ 22.8  
Deferred                 (28.8) 774.8 800.1  
Total Federal                 (41.9) 882.1 822.9  
State and Local:                        
Current                 (10.5) 14.5 22.8  
Deferred                 (21.2) 23.0 56.9  
Total State and Local                 (31.8) 37.5 79.7  
Income Tax Expense (Credit)                 (73.7) 919.6 902.6  
Income Tax Expense:                        
Deferred                 (50.0) 808.2 868.8  
Income Tax Expense (Credit)                 (73.7) 919.6 902.6  
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income $ 375.2 $ (764.2) [1] $ 503.9 $ 503.1 $ 470.7 $ 519.6 $ 431.3 $ 630.7 618.0 2,052.3 1,638.0  
Discontinued Operations     2.5 [2]   (265.5) [3] (7.8) 0.1 (10.5) 2.5 (283.7) (47.5)  
Income Tax Expense (Credit)                 (73.7) 919.6 902.6  
Pretax Income                 546.8 2,688.2 2,493.1  
Income Taxes on Pretax Income at Statutory Rate (35%)                 191.4 940.9 872.6  
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                 41.7 53.6 54.0  
Investment Tax Credits, Net                 (12.3) (11.6) (12.8)  
State and Local Income Taxes, Net                 (20.7) 24.4 54.3  
Removal Costs                 (39.8) (28.8) (23.9)  
AFUDC                 (44.8) (51.6) (41.8)  
Valuation Allowance                 (128.3) 17.2 (2.5)  
Tax Adjustments                 (43.9) (20.1) (10.1)  
U.K. Windfall Tax                 (12.9) 0.0 0.0  
Other                 (4.1) (4.4) 12.8  
Income Tax Expense (Credit)                 $ (73.7) $ 919.6 $ 902.6  
Effective Income Tax Rate                 (13.47842%) 34.20876% 36.20392%  
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 2,753.0       2,503.9       $ 2,753.0 $ 2,503.9    
Deferred Tax Liabilities (14,637.4)       (14,237.1)       (14,637.4) (14,237.1)    
Property Related Temporary Differences (8,758.1)       (8,533.3)       (8,758.1) (8,533.3)    
Amounts Due from Customers for Future Federal Income Taxes (292.2)       (263.5)       (292.2) (263.5)    
Deferred State Income Taxes (976.6)       (872.0)       (976.6) (872.0)    
Securitized Assets (535.6)       (633.2)       (535.6) (633.2)    
Regulatory Assets (896.9)       (873.6)       (896.9) (873.6)    
Deferred Income Taxes on Other Comprehensive Loss 88.7       72.2       88.7 72.2    
Accrued Nuclear Decommissioning (666.8)       (614.6)       (666.8) (614.6)    
Net Operating Loss Carryforward 101.2       39.6       101.2 39.6    
Tax Credit Carryforward 45.1       85.0       45.1 85.0    
Valuation Allowance (1.8)       (130.0)       (1.8) (130.0)    
All Other, Net 8.6       (9.8)       8.6 (9.8)    
Net Deferred Tax Liabilities (11,884.4)       (11,733.2)       (11,884.4) (11,733.2)    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                 2.7 2.7 $ 2.9  
Interest Income                 9.9 0.8 1.2  
Reversal of Prior Period Interest Expense                 3.3 0.0 2.0  
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 2.9       44.7       2.9 44.7    
Accrual for Payment of Interest and Penalties 5.8       7.2       5.8 7.2    
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       187.0       182.0 187.0 182.0 175.2  
Increase - Tax Positions Taken During a Prior Period                 86.0 5.4 18.2  
Decrease - Tax Positions Taken During a Prior Period                 (161.2) (0.4) (1.5)  
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                 (13.0) 0.0 (0.6)  
Decrease - Lapse of the Applicable Statute of Limitations                 0.0 0.0 (9.3)  
Balance at December 31, 98.8       187.0       98.8 187.0 182.0 $ 175.2
Unrecognized Tax Benefits, if Recognized - Amount 15.8       100.2       $ 15.8 $ 100.2 $ 97.2  
Income Taxes (Textuals) [Abstract]                        
Statutory Tax Rate on Pretax Income                 35.00% 35.00% 35.00%  
Federal Net Income Tax Operating Loss                 $ 143.0      
Income Tax Expense (Credit)                 (73.7) $ 919.6 $ 902.6  
Interest Income                 16.3 7.9 7.4  
Net Income (Loss) 375.2 (764.2) [1] 503.9 503.1 470.7 519.6 431.3 630.7 $ 618.0 2,052.3 $ 1,638.0  
Period with No Change in Unrecognized Tax Benefits                 12 months      
Original Indiana Corporate Income Tax Rate                 8.50%      
Reduced Indiana Corporate Income Tax Rate                 6.50%      
Reduction In Indiana Corporate Tax Rate                 0.50%      
Indiana Corporate Tax Rate                 4.90%      
Original WV Corporate Income Tax Rate                     7.00%  
Reduced WV Corporate Income Tax                     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 (1.8)       (130.0)       $ (1.8) (130.0)    
Transmission and Distribution Expenses Net Income Adjustment                 21.0      
Appalachian Power Co [Member]                        
Federal:                        
Current                 64.1      
Deferred                 125.8      
Deferred Investment Tax Credits                   (0.3) $ (0.7)  
Total Federal                 189.8      
State and Local:                        
Current                 4.4      
Deferred                 4.9      
Deferred Investment Tax Credits                   (0.3) (0.7)  
Total State and Local                 9.3      
Income Tax Expense (Credit)                 199.1 194.3 154.9  
Income Tax Expense:                        
Current                   (32.9) 10.9  
Deferred                 130.7 227.5 144.7  
Deferred Investment Tax Credits                   (0.3) (0.7)  
Income Tax Expense (Credit)                 199.1 194.3 154.9  
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 65.3 104.1 73.4 126.3 65.2 74.6 59.0 141.8 369.1 340.6 215.4  
Discontinued Operations     0.0   0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                 199.1 194.3 154.9  
Pretax Income                 568.2 534.9 370.3  
Income Taxes on Pretax Income at Statutory Rate (35%)                 198.9 187.2 129.6  
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                 19.3 19.8 23.5  
Investment Tax Credits, Net                 (0.1) (0.3) (0.6)  
State and Local Income Taxes, Net                 6.0 7.2 6.5  
Removal Costs                 (12.0) (9.9) (6.8)  
AFUDC                 (6.1) (7.0) (3.8)  
Valuation Allowance                 (1.7) 1.7 (2.5)  
Other                 (5.2) (4.4) 9.0  
Income Tax Expense (Credit)                 $ 199.1 $ 194.3 $ 154.9  
Effective Income Tax Rate                 35.04048% 36.32455% 41.83095%  
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 413.5       412.9       $ 413.5 $ 412.9    
Deferred Tax Liabilities (3,085.8)       (2,939.9)       (3,085.8) (2,939.9)    
Property Related Temporary Differences (2,031.9)       (1,866.0)       (2,031.9) (1,866.0)    
Amounts Due from Customers for Future Federal Income Taxes (73.1)       (68.2)       (73.1) (68.2)    
Deferred State Income Taxes (319.3)       (308.7)       (319.3) (308.7)    
Securitized Assets (106.9)       (114.8)       (106.9) (114.8)    
Regulatory Assets (159.9)       (169.1)       (159.9) (169.1)    
Deferred Income Taxes on Other Comprehensive Loss 4.5       1.5       4.5 1.5    
Tax Credit Carryforward 11.7       19.2       11.7 19.2    
All Other, Net 2.6       (20.9)       2.6 (20.9)    
Net Deferred Tax Liabilities (2,672.3)       (2,527.0)       (2,672.3) (2,527.0)    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                 0.0 0.4 $ 0.0  
Interest Income                 0.1 0.0 0.0  
Reversal of Prior Period Interest Expense                 0.0 0.0 0.2  
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 0.1       0.0       0.1 0.0    
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       0.3       0.0 0.3 0.0 1.2  
Increase - Tax Positions Taken During a Prior Period                 0.0 0.3 0.0  
Decrease - Tax Positions Taken During a Prior Period                 (0.3) 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 (1.2)  
Balance at December 31, 0.0       0.3       0.0 0.3 0.0 1.2
Unrecognized Tax Benefits, if Recognized - Amount 0.0       0.2       $ 0.0 $ 0.2 $ 0.0  
Income Taxes (Textuals) [Abstract]                        
Statutory Tax Rate on Pretax Income                 35.00% 35.00% 35.00%  
Income Tax Expense (Credit)                 $ 199.1 $ 194.3 $ 154.9  
Net Income (Loss) 65.3 104.1 73.4 126.3 65.2 74.6 59.0 141.8 $ 369.1 340.6 $ 215.4  
Period with No Change in Unrecognized Tax Benefits                 12 months      
Original Indiana Corporate Income Tax Rate                 8.50%      
Reduced Indiana Corporate Income Tax Rate                 6.50%      
Reduction In Indiana Corporate Tax Rate                 0.50%      
Indiana Corporate Tax Rate                 4.90%      
Original WV Corporate Income Tax Rate                     7.00%  
Reduced WV Corporate Income Tax                     6.50%  
Indiana Michigan Power Co [Member]                        
Federal:                        
Current                 $ (44.8)      
Deferred                 104.9      
Deferred Investment Tax Credits                   (3.3) $ (4.9)  
Total Federal                 63.9      
State and Local:                        
Current                 3.4      
Deferred                 0.2      
Deferred Investment Tax Credits                   (3.3) (4.9)  
Total State and Local                 3.6      
Income Tax Expense (Credit)                 67.5 96.1 79.6  
Income Tax Expense:                        
Current                   5.2 14.3  
Deferred                 105.1 94.2 70.2  
Deferred Investment Tax Credits                   (3.3) (4.9)  
Income Tax Expense (Credit)                 67.5 96.1 79.6  
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 38.5 75.4 51.3 74.7 24.9 56.6 50.6 72.7 239.9 204.8 155.6  
Discontinued Operations     0.0   0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                 67.5 96.1 79.6  
Pretax Income                 307.4 300.9 235.2  
Income Taxes on Pretax Income at Statutory Rate (35%)                 107.6 105.3 82.3  
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                 6.7 9.5 12.9  
Investment Tax Credits, Net                 (4.7) (3.3) (4.9)  
State and Local Income Taxes, Net                 2.4 5.8 7.7  
Removal Costs                 (21.3) (12.6) (11.3)  
AFUDC                 (7.3) (6.2) (10.0)  
Tax Adjustments                 (14.2) (4.2) 1.2  
Other                 (1.7) 1.8 1.7  
Income Tax Expense (Credit)                 $ 67.5 $ 96.1 $ 79.6  
Effective Income Tax Rate                 21.95836% 31.93752% 33.84354%  
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 912.9       837.4       $ 912.9 $ 837.4    
Deferred Tax Liabilities (2,440.3)       (2,198.9)       (2,440.3) (2,198.9)    
Property Related Temporary Differences (579.4)       (521.6)       (579.4) (521.6)    
Amounts Due from Customers for Future Federal Income Taxes (50.4)       (42.7)       (50.4) (42.7)    
Deferred State Income Taxes (158.7)       (124.8)       (158.7) (124.8)    
Regulatory Assets (81.0)       (70.2)       (81.0) (70.2)    
Deferred Income Taxes on Other Comprehensive Loss 8.8       9.0       8.8 9.0    
Accrued Nuclear Decommissioning (666.8)       (614.6)       (666.8) (614.6)    
Net Operating Loss Carryforward 7.1       0.0       7.1 0.0    
All Other, Net (7.0)       3.4       (7.0) 3.4    
Net Deferred Tax Liabilities (1,527.4)       (1,361.5)       (1,527.4) (1,361.5)    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                 0.2 0.2 $ 0.0  
Interest Income                 0.0 0.0 0.0  
Reversal of Prior Period Interest Expense                 0.0 0.0 0.3  
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 0.9       0.6       0.9 0.6    
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       2.4       2.3 2.4 2.3 3.2  
Increase - Tax Positions Taken During a Prior Period                 1.8 0.1 1.4  
Decrease - Tax Positions Taken During a Prior Period                 (0.4) 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 (0.7)  
Decrease - Lapse of the Applicable Statute of Limitations                 0.0 0.0 (1.6)  
Balance at December 31, 3.8       2.4       3.8 2.4 2.3 3.2
Unrecognized Tax Benefits, if Recognized - Amount 2.5       1.6       $ 2.5 $ 1.6 $ 1.6  
Income Taxes (Textuals) [Abstract]                        
Statutory Tax Rate on Pretax Income                 35.00% 35.00% 35.00%  
Federal Net Income Tax Operating Loss                 $ 20.0      
Income Tax Expense (Credit)                 67.5 $ 96.1 $ 79.6  
Net Income (Loss) 38.5 75.4 51.3 74.7 24.9 56.6 50.6 72.7 $ 239.9 204.8 $ 155.6  
Period with No Change in Unrecognized Tax Benefits                 12 months      
Original Indiana Corporate Income Tax Rate                 8.50%      
Reduced Indiana Corporate Income Tax Rate                 6.50%      
Reduction In Indiana Corporate Tax Rate                 0.50%      
Indiana Corporate Tax Rate                 4.90%      
Original WV Corporate Income Tax Rate                     7.00%  
Reduced WV Corporate Income Tax                     6.50%  
Ohio Power Co [Member]                        
Federal:                        
Current                 $ 178.8      
Deferred                 (40.8)      
Deferred Investment Tax Credits                   (0.1) $ (0.3)  
Total Federal                 138.0      
State and Local:                        
Current                 4.2      
Deferred                 1.6      
Deferred Investment Tax Credits                   (0.1) (0.3)  
Total State and Local                 5.8      
Income Tax Expense (Credit)                 143.8 126.5 132.2  
Income Tax Expense:                        
Current                   89.0 58.1  
Deferred                 (39.2) 37.6 74.4  
Deferred Investment Tax Credits                   (0.1) (0.3)  
Income Tax Expense (Credit)                 143.8 126.5 132.2  
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 37.5 99.9 74.6 70.2 48.0 71.6 47.7 65.4 282.2 232.7 216.4  
Discontinued Operations     0.0   0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                 143.8 126.5 132.2  
Pretax Income                 426.0 359.2 348.6  
Income Taxes on Pretax Income at Statutory Rate (35%)                 149.1 125.7 122.0  
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                 7.1 8.2 6.7  
Investment Tax Credits, Net                 0.0 (0.1) (0.2)  
State and Local Income Taxes, Net                 3.8 0.7 8.8  
Other                 (16.2) (8.0) (5.1)  
Income Tax Expense (Credit)                 $ 143.8 $ 126.5 $ 132.2  
Effective Income Tax Rate                 33.75587% 35.21715% 37.92312%  
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 232.4       162.4       $ 232.4 $ 162.4    
Deferred Tax Liabilities (1,578.5)       (1,545.6)       (1,578.5) (1,545.6)    
Property Related Temporary Differences (1,090.8)       (1,022.8)       (1,090.8) (1,022.8)    
Amounts Due from Customers for Future Federal Income Taxes (43.6)       (44.6)       (43.6) (44.6)    
Deferred State Income Taxes (34.6)       (34.4)       (34.6) (34.4)    
Regulatory Assets (174.1)       (220.0)       (174.1) (220.0)    
Deferred Income Taxes on Other Comprehensive Loss (1.6)       (2.3)       (1.6) (2.3)    
Deferred Fuel and Purchased Power (117.6)       (117.4)       (117.6) (117.4)    
All Other, Net 116.2       58.3       116.2 58.3    
Net Deferred Tax Liabilities (1,346.1)       (1,383.2)       (1,346.1) (1,383.2)    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                 0.2 1.0 $ 0.1  
Interest Income                 0.0 0.0 0.0  
Reversal of Prior Period Interest Expense                 0.0 0.0 0.2  
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 1.7       0.6       1.7 0.6    
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       6.9       6.9 6.9 6.9 2.1  
Increase - Tax Positions Taken During a Prior Period                 0.0 0.0 6.4  
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 (1.6)  
Balance at December 31, 6.9       6.9       6.9 6.9 6.9 2.1
Unrecognized Tax Benefits, if Recognized - Amount 4.4       4.5       $ 4.4 $ 4.5 $ 4.5  
Income Taxes (Textuals) [Abstract]                        
Statutory Tax Rate on Pretax Income                 35.00% 35.00% 35.00%  
Income Tax Expense (Credit)                 $ 143.8 $ 126.5 $ 132.2  
Net Income (Loss) 37.5 99.9 74.6 70.2 48.0 71.6 47.7 65.4 $ 282.2 232.7 $ 216.4  
Period with No Change in Unrecognized Tax Benefits                 12 months      
Original Indiana Corporate Income Tax Rate                 8.50%      
Reduced Indiana Corporate Income Tax Rate                 6.50%      
Reduction In Indiana Corporate Tax Rate                 0.50%      
Indiana Corporate Tax Rate                 4.90%      
Original WV Corporate Income Tax Rate                     7.00%  
Reduced WV Corporate Income Tax                     6.50%  
Public Service Co Of Oklahoma [Member]                        
Federal:                        
Current                 $ (28.0)      
Deferred                 77.2      
Deferred Investment Tax Credits                   (0.6) $ 0.1  
Total Federal                 47.8      
State and Local:                        
Current                 (1.9)      
Deferred                 5.3      
Deferred Investment Tax Credits                   (0.6) 0.1  
Total State and Local                 6.6      
Income Tax Expense (Credit)                 54.4 51.3 50.6  
Income Tax Expense:                        
Current                   (6.4) (24.2)  
Deferred                 82.5 58.3 74.7  
Deferred Investment Tax Credits                   (0.6) 0.1  
Income Tax Expense (Credit)                 54.4 51.3 50.6  
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 2.6 52.8 28.9 15.7 7.0 44.7 27.1 13.7 100.0 92.5 86.9  
Discontinued Operations     0.0   0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                 54.4 51.3 50.6  
Pretax Income                 154.4 143.8 137.5  
Income Taxes on Pretax Income at Statutory Rate (35%)                 54.0 50.3 48.1  
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                 0.8 0.5 0.2  
Investment Tax Credits, Net                 (1.4) (1.8) (0.8)  
State and Local Income Taxes, Net                 4.2 5.1 4.8  
AFUDC                 (2.2) (3.1) (1.1)  
Other                 (1.0) 0.3 (0.6)  
Income Tax Expense (Credit)                 $ 54.4 $ 51.3 $ 50.6  
Effective Income Tax Rate                 35.23316% 35.67455% 36.80%  
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 153.8       141.2       $ 153.8 $ 141.2    
Deferred Tax Liabilities (1,212.6)       (1,113.0)       (1,212.6) (1,113.0)    
Property Related Temporary Differences (927.3)       (861.9)       (927.3) (861.9)    
Amounts Due from Customers for Future Federal Income Taxes (3.2)       (2.2)       (3.2) (2.2)    
Deferred State Income Taxes (128.5)       (117.0)       (128.5) (117.0)    
Regulatory Assets (67.6)       (54.3)       (67.6) (54.3)    
Deferred Income Taxes on Other Comprehensive Loss (1.8)       (2.3)       (1.8) (2.3)    
Deferred Federal Income Taxes on Deferred State Income Taxes 50.6       46.6       50.6 46.6    
Net Operating Loss Carryforward 16.5       7.1       16.5 7.1    
Tax Credit Carryforward 0.0       0.6       0.0 0.6    
All Other, Net 2.5       11.6       2.5 11.6    
Net Deferred Tax Liabilities (1,058.8)       (971.8)       (1,058.8) (971.8)    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                 0.0 0.1 $ 0.1  
Interest Income                 0.3 0.0 0.0  
Reversal of Prior Period Interest Expense                 0.7 0.0 0.1  
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.6       0.0       0.6 0.0    
Accrual for Payment of Interest and Penalties 0.0       0.4       0.0 0.4    
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       1.3       1.3 1.3 1.3 2.2  
Increase - Tax Positions Taken During a Prior Period                 0.1 0.0 0.0  
Decrease - Tax Positions Taken During a Prior Period                 (1.3) 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 (0.9)  
Balance at December 31, 0.1       1.3       0.1 1.3 1.3 2.2
Unrecognized Tax Benefits, if Recognized - Amount 0.1       0.9       $ 0.1 $ 0.9 $ 0.9  
Income Taxes (Textuals) [Abstract]                        
Statutory Tax Rate on Pretax Income                 35.00% 35.00% 35.00%  
Federal Net Income Tax Operating Loss                 $ 17.0      
Income Tax Expense (Credit)                 54.4 $ 51.3 $ 50.6  
Net Income (Loss) 2.6 52.8 28.9 15.7 7.0 44.7 27.1 13.7 $ 100.0 92.5 86.9  
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:                        
Current                 (96.7)      
Deferred                 172.6      
Deferred Investment Tax Credits                   (1.4) (1.4)  
Total Federal                 74.7      
State and Local:                        
Current                 (12.6)      
Deferred                 (10.0)      
Deferred Investment Tax Credits                   (1.4) (1.4)  
Total State and Local                 (22.6)      
Income Tax Expense (Credit)                 52.1 84.8 66.4  
Income Tax Expense:                        
Current                   44.3 (171.6)  
Deferred                 162.6 41.9 239.4  
Deferred Investment Tax Credits                   (1.4) (1.4)  
Income Tax Expense (Credit)                 52.1 84.8 66.4  
Reconciliation of Federal Income Taxes and Amount of Income Tax Reported                        
Net Income 16.5 84.4 44.3 24.5 7.7 82.1 59.5 46.7 169.7 196.0 144.6  
Discontinued Operations     0.0   0.0 0.0 0.0 0.0        
Income Tax Expense (Credit)                 52.1 84.8 66.4  
Pretax Income                 221.8 280.8 211.0  
Income Taxes on Pretax Income at Statutory Rate (35%)                 77.6 98.3 73.8  
Reconciliation of Federal Statutory Rate and Amount of Taxes Reported                        
Depreciation                 3.2 3.1 2.9  
Depletion                 (5.5) (5.5) (4.1)  
Investment Tax Credits, Net                 (1.2) (1.4) (1.4)  
State and Local Income Taxes, Net                 (14.7) 4.8 3.1  
AFUDC                 (3.9) (9.2) (4.2)  
Other                 (3.4) (5.3) (3.7)  
Income Tax Expense (Credit)                 $ 52.1 $ 84.8 $ 66.4  
Effective Income Tax Rate                 23.48963% 30.19943% 31.46919%  
Net Deferred Tax Liability and Significant Temporary Differences                        
Deferred Tax Assets 230.5       194.7       $ 230.5 $ 194.7    
Deferred Tax Liabilities (1,837.4)       (1,594.5)       (1,837.4) (1,594.5)    
Property Related Temporary Differences (1,445.2)       (1,275.1)       (1,445.2) (1,275.1)    
Amounts Due from Customers for Future Federal Income Taxes (48.2)       (47.8)       (48.2) (47.8)    
Deferred State Income Taxes (175.1)       (132.3)       (175.1) (132.3)    
Regulatory Assets (40.7)       (26.1)       (40.7) (26.1)    
Deferred Income Taxes on Other Comprehensive Loss 5.1       5.0       5.1 5.0    
Impairment Loss 20.3       20.7       20.3 20.7    
Net Operating Loss Carryforward 40.3       19.7       40.3 19.7    
Tax Credit Carryforward 0.1       0.7       0.1 0.7    
All Other, Net 36.5       35.4       36.5 35.4    
Net Deferred Tax Liabilities (1,606.9)       (1,399.8)       (1,606.9) (1,399.8)    
Summary of Amounts Reported for Interest Expense, Interest Income and Reversal of Prior Period Interest Expense                        
Interest Expense                 0.0 0.4 $ 0.2  
Interest Income                 0.0 0.0 0.0  
Reversal of Prior Period Interest Expense                 1.4 0.0 0.2  
Amounts Accrued for Receipt of Interest and Payment of Interest and Penalties                        
Accrual for Receipt of Interest 0.1       0.0       0.1 0.0    
Accrual for Payment of Interest and Penalties 0.0       1.4       0.0 1.4    
Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits                        
Balance at January 1,       9.3       7.5 9.3 7.5 7.6  
Increase - Tax Positions Taken During a Prior Period                 1.3 1.8 1.6  
Decrease - Tax Positions Taken During a Prior Period                 (9.3) 0.0 (0.8)  
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 (0.9)  
Balance at December 31, 1.3       9.3       1.3 9.3 7.5 7.6
Unrecognized Tax Benefits, if Recognized - Amount 0.8       6.0       $ 0.8 $ 6.0 $ 4.9  
Income Taxes (Textuals) [Abstract]                        
Statutory Tax Rate on Pretax Income                 35.00% 35.00% 35.00%  
Federal Net Income Tax Operating Loss                 $ 37.0      
Income Tax Expense (Credit)                 52.1 $ 84.8 $ 66.4  
Net Income (Loss) 16.5 $ 84.4 $ 44.3 $ 24.5 7.7 $ 82.1 $ 59.5 $ 46.7 $ 169.7 196.0 144.6  
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      
Arkansas [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 16.7               $ 16.7      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2021      
Arkansas [Member] | Southwestern Electric Power Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 16.2               $ 16.2      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2021      
Kentucky [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 89.7               $ 89.7      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Louisiana [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 509.1               $ 509.1      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Louisiana [Member] | Southwestern Electric Power Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 508.3               $ 508.3      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Missouri [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 6.3               $ 6.3      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Oklahoma [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 529.9               $ 529.9      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Oklahoma [Member] | Public Service Co Of Oklahoma [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 273.2               $ 273.2      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Oklahoma [Member] | Southwestern Electric Power Co [Member]                        
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 4.2               $ 4.2      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Federal [Member]                        
Federal:                        
Deferred Investment Tax Credits                 $ 17.6      
State and Local:                        
Deferred Investment Tax Credits                 17.6      
Income Tax Expense:                        
Deferred Investment Tax Credits                 17.6      
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 50.0               $ 50.0      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 53.6               $ 53.6      
Tax Credit Carryforward Amount To Expire If Not Used 34.3               34.3      
Income Taxes (Textuals) [Abstract]                        
Uncertain Tax Positions Netted Against Operating Loss Carryforward                       121.0
Uncertain Tax Position Noncurrent                     $ 69.0  
Uncertain Tax Positions Netted Against Tax Credit and Alternative Minimum Tax Carryforward Tax Benefits 17.0       59.0       $ 17.0 $ 59.0    
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] | Appalachian Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                 $ (0.1)      
State and Local:                        
Deferred Investment Tax Credits                 (0.1)      
Income Tax Expense:                        
Deferred Investment Tax Credits                 (0.1)      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 11.7               11.7      
Tax Credit Carryforward Amount To Expire If Not Used 4.5               $ 4.5      
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                 $ 3.8      
State and Local:                        
Deferred Investment Tax Credits                 3.8      
Income Tax Expense:                        
Deferred Investment Tax Credits                 3.8      
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 7.0               $ 7.0      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 9.0               $ 9.0      
Tax Credit Carryforward Amount To Expire If Not Used 8.5               $ 8.5      
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      
State and Local:                        
Deferred Investment Tax Credits                 0.0      
Income Tax Expense:                        
Deferred Investment Tax Credits                 0.0      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 8.6               8.6      
Tax Credit Carryforward Amount To Expire If Not Used 0.0               $ 0.0      
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                 $ (1.4)      
State and Local:                        
Deferred Investment Tax Credits                 (1.4)      
Income Tax Expense:                        
Deferred Investment Tax Credits                 (1.4)      
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 6.0               $ 6.0      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.0               $ 0.0      
Tax Credit Carryforward Amount To Expire If Not Used 0.0               $ 0.0      
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                 $ (1.2)      
State and Local:                        
Deferred Investment Tax Credits                 (1.2)      
Income Tax Expense:                        
Deferred Investment Tax Credits                 (1.2)      
Net Income Tax Operating Loss Carryforwards                        
Net Income Tax Operating Loss Carryforward 13.0               $ 13.0      
Operating Loss Carryforwards, Expiration Date                 Dec. 31, 2036      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 0.1               $ 0.1      
Tax Credit Carryforward Amount To Expire If Not Used 0.0               $ 0.0      
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      
State [Member]                        
Federal:                        
Deferred Investment Tax Credits                 $ (0.1)      
State and Local:                        
Deferred Investment Tax Credits                 (0.1)      
Income Tax Expense:                        
Deferred Investment Tax Credits                 (0.1)      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 26.6               26.6      
Tax Credit Carryforward Amount To Expire If Not Used 26.6               26.6      
State [Member] | Appalachian Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                 0.0      
State and Local:                        
Deferred Investment Tax Credits                 0.0      
Income Tax Expense:                        
Deferred Investment Tax Credits                 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      
State [Member] | Indiana Michigan Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                 0.0      
State and Local:                        
Deferred Investment Tax Credits                 0.0      
Income Tax Expense:                        
Deferred Investment Tax Credits                 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      
State [Member] | Ohio Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                 0.0      
State and Local:                        
Deferred Investment Tax Credits                 0.0      
Income Tax Expense:                        
Deferred Investment Tax Credits                 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      
State [Member] | Public Service Co Of Oklahoma [Member]                        
Federal:                        
Deferred Investment Tax Credits                 3.2      
State and Local:                        
Deferred Investment Tax Credits                 3.2      
Income Tax Expense:                        
Deferred Investment Tax Credits                 3.2      
Tax Credit Carryforward                        
Tax Credit Carryforward, Amount 26.6               26.6      
Tax Credit Carryforward Amount To Expire If Not Used 26.6               26.6      
State [Member] | Southwestern Electric Power Co [Member]                        
Federal:                        
Deferred Investment Tax Credits                 0.0      
State and Local:                        
Deferred Investment Tax Credits                 0.0      
Income Tax Expense:                        
Deferred Investment Tax Credits                 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      
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]                        
Income Taxes (Textuals) [Abstract]                        
Bonus Depreciation Extension                     50.00%  
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] | 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 $ 6.2 $ 39.0  
Expiration of Charitable Contribution Carryforward Deductions [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance (6.0)       (17.0)       (6.0) (17.0)    
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance (6.0)       (17.0)       (6.0) (17.0)    
Investment in Operations of AEPRO [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance         (156.0)         (156.0)    
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance         (156.0)         (156.0)    
Sale of AEPRO [Member]                        
Net Deferred Tax Liability and Significant Temporary Differences                        
Valuation Allowance         (48.0)         (48.0)    
Income Taxes (Textuals) [Abstract]                        
Valuation Allowance         $ (48.0)         $ (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)      
[1] Includes impairments for Merchant Generating Assets (see Note 7).
[2] Includes final accounting adjustment for sale of AEPRO (see Note 7).
[3] Includes sale of AEPRO (see Note 7).