Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Expense (Benefit)	$ (72.2)	$ (190.6)	$ (174.2)	$ (533.8)
Increase in Current Liabilities			(112.3)	(288.9)
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 185.1	$ 132.0
Effective Income Tax Rate	12.00%	34.60%	15.00%	36.50%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
Kentucky Net Operating Loss Limitation Percent	80.00%
Kentucky Single Corporate Tax Rate	5.00%
Net Regulatory Liability for Tax Reform [Member]
Income Taxes (Textuals)
Excess Accumulated Deferred Income Taxes			$ 4,400.0
Incremental Liability for Tax Reform [Member]
Income Taxes (Textuals)
Excess Accumulated Deferred Income Taxes			1,200.0
Pretax Excess ADIT [Member]
Income Taxes (Textuals)
Excess Accumulated Deferred Income Taxes			4,400.0
Temporary Differences Associated with Depreciable Property [Member]
Income Taxes (Textuals)
Excess Accumulated Deferred Income Taxes			3,400.0
Remaining Excess ADIT [Member]
Income Taxes (Textuals)
Excess Accumulated Deferred Income Taxes			1,000.0
AEP Texas Inc. [Member]
Income Tax Expense (Benefit)	$ (9.0)	$ (25.9)	(18.1)	$ (43.6)
Increase in Current Liabilities			(5.5)	(31.0)
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 21.6	$ 5.9
Effective Income Tax Rate	16.20%	34.60%	16.20%	34.60%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
AEP Transmission Co [Member]
Income Tax Expense (Benefit)	$ (20.0)	$ (55.8)	$ (42.5)	$ (84.3)
Increase in Current Liabilities			(28.2)	1.0
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 17.8	$ 17.0
Effective Income Tax Rate	22.10%	34.20%	21.40%	33.90%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
Kentucky Net Operating Loss Limitation Percent	80.00%
Kentucky Single Corporate Tax Rate	5.00%
Appalachian Power Co [Member]
Income Tax Expense (Benefit)	$ (15.8)	$ (29.9)	$ (43.8)	$ (93.5)
Increase in Current Liabilities			(21.9)	(14.1)
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 68.7	$ 13.7
Effective Income Tax Rate	17.00%	36.50%	17.80%	36.50%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
Indiana Michigan Power Co [Member]
Income Tax Expense (Benefit)	$ (0.7)	$ (4.0)	$ (13.1)	$ (33.2)
Increase in Current Liabilities			(19.3)	(29.5)
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 44.4	$ 34.8
Effective Income Tax Rate	0.70%	27.60%	7.60%	29.60%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
Kentucky Net Operating Loss Limitation Percent	80.00%
Kentucky Single Corporate Tax Rate	5.00%
Ohio Power Co [Member]
Income Tax Expense (Benefit)	$ (19.0)	$ (33.4)	$ (39.5)	$ (79.7)
Increase in Current Liabilities			(11.4)	(25.3)
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 56.0	$ 41.8
Effective Income Tax Rate	21.60%	34.90%	21.00%	34.90%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
Kentucky Net Operating Loss Limitation Percent	80.00%
Kentucky Single Corporate Tax Rate	5.00%
Public Service Co Of Oklahoma [Member]
Income Tax Expense (Benefit)	$ (6.4)	$ (12.3)	$ (5.0)	$ (15.2)
Increase in Current Liabilities			3.0	(26.0)
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 14.8	$ (0.7)
Effective Income Tax Rate	14.90%	37.60%	14.50%	37.60%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
Southwestern Electric Power Co [Member]
Income Tax Expense (Benefit)	$ (5.4)	$ (13.2)	$ (8.3)	$ (22.7)
Increase in Current Liabilities			10.5	(24.1)
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 45.4	$ (11.1)
Effective Income Tax Rate	12.40%	29.70%	14.00%	32.40%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate	21.00%	35.00%	21.00%	35.00%
Reduction in Corporate Federal Income Tax Rate [Member]
Increase in Current Liabilities			$ 0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			143.6
Reduction in Corporate Federal Income Tax Rate [Member] | AEP Texas Inc. [Member]
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			18.0
Reduction in Corporate Federal Income Tax Rate [Member] | AEP Transmission Co [Member]
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			5.7
Reduction in Corporate Federal Income Tax Rate [Member] | Appalachian Power Co [Member]
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			48.8
Reduction in Corporate Federal Income Tax Rate [Member] | Indiana Michigan Power Co [Member]
Increase in Current Liabilities			4.0
Increase in Deferred Credits and Other Noncurrent Liabilities			10.3
Reduction in Corporate Federal Income Tax Rate [Member] | Ohio Power Co [Member]
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			27.8
Reduction in Corporate Federal Income Tax Rate [Member] | Public Service Co Of Oklahoma [Member]
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			4.7
Reduction in Corporate Federal Income Tax Rate [Member] | Southwestern Electric Power Co [Member]
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			24.2
Excess ADIT [Member]
Decrease in Total Revenue			(33.3)
Increase in Current Liabilities			1.2
Increase in Deferred Credits and Other Noncurrent Liabilities			32.1
Excess ADIT [Member] | AEP Texas Inc. [Member]
Decrease in Total Revenue			(4.9)
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			4.9
Excess ADIT [Member] | AEP Transmission Co [Member]
Decrease in Total Revenue			(0.2)
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			0.2
Excess ADIT [Member] | Appalachian Power Co [Member]
Decrease in Total Revenue			(9.6)
Increase in Current Liabilities			0.4
Increase in Deferred Credits and Other Noncurrent Liabilities			9.2
Excess ADIT [Member] | Indiana Michigan Power Co [Member]
Decrease in Total Revenue			(1.2)
Increase in Current Liabilities			0.3
Increase in Deferred Credits and Other Noncurrent Liabilities			0.9
Excess ADIT [Member] | Ohio Power Co [Member]
Decrease in Total Revenue			(2.5)
Increase in Current Liabilities			0.3
Increase in Deferred Credits and Other Noncurrent Liabilities			2.2
Excess ADIT [Member] | Public Service Co Of Oklahoma [Member]
Decrease in Total Revenue			(4.6)
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			4.6
Excess ADIT [Member] | Southwestern Electric Power Co [Member]
Decrease in Total Revenue			(7.0)
Increase in Current Liabilities			0.0
Increase in Deferred Credits and Other Noncurrent Liabilities			$ 7.0
IRS Audit Settlement [Member]
Reversed Unrecognized Tax Benefit	$ 72.0
Remeasurement of Kentucky Deferred Taxes [Member]
Income Tax Expense (Benefit)	$ 18.0