Income Taxes (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 26, 2018	Mar. 31, 2018	Mar. 31, 2017
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ (63.2)	$ (289.3)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 133.3	$ 45.0
Effective Income Tax Rate		18.30%	36.70%
Kentucky Maximum Graduated Corporate Tax Rate		6.00%
Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (119.5)
Increase in Current Liabilities		33.9
Increase in Deferred Credits and Other Noncurrent Liabilities		85.6
Excess ADIT [Member]
Decrease in Total Revenue		(17.2)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 17.2
AEP Texas Inc. [Member]
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ (5.1)	$ (25.9)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 6.5	$ 4.8
Effective Income Tax Rate		16.30%	34.70%
AEP Texas Inc. [Member] | Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (7.6)
Increase in Current Liabilities		0.0
Increase in Deferred Credits and Other Noncurrent Liabilities		7.6
AEP Texas Inc. [Member] | Excess ADIT [Member]
Decrease in Total Revenue		(2.1)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 2.1
AEP Transmission Co [Member]
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ 0.6	$ 0.0
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 23.9	$ 8.3
Effective Income Tax Rate		20.80%	33.30%
Kentucky Maximum Graduated Corporate Tax Rate		6.00%
AEP Transmission Co [Member] | Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (19.0)
Increase in Current Liabilities		16.2
Increase in Deferred Credits and Other Noncurrent Liabilities		2.8
AEP Transmission Co [Member] | Excess ADIT [Member]
Decrease in Total Revenue		(0.1)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 0.1
Appalachian Power Co [Member]
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ 5.6	$ (3.5)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 37.9	$ (3.7)
Effective Income Tax Rate		18.20%	36.50%
Appalachian Power Co [Member] | Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (35.4)
Increase in Current Liabilities		7.8
Increase in Deferred Credits and Other Noncurrent Liabilities		27.6
Appalachian Power Co [Member] | Excess ADIT [Member]
Decrease in Total Revenue		(4.6)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 4.6
Indiana Michigan Power Co [Member]
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ (27.8)	$ (41.2)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 33.7	$ 13.5
Effective Income Tax Rate		16.20%	29.90%
Kentucky Maximum Graduated Corporate Tax Rate		6.00%
Indiana Michigan Power Co [Member] | Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (17.8)
Increase in Current Liabilities		3.0
Increase in Deferred Credits and Other Noncurrent Liabilities		14.8
Indiana Michigan Power Co [Member] | Excess ADIT [Member]
Decrease in Total Revenue		(1.7)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 1.7
Ohio Power Co [Member]
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ (2.9)	$ (31.2)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 40.6	$ 30.6
Effective Income Tax Rate		20.50%	34.90%
Kentucky Maximum Graduated Corporate Tax Rate		6.00%
Ohio Power Co [Member] | Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (21.3)
Increase in Current Liabilities		6.2
Increase in Deferred Credits and Other Noncurrent Liabilities		15.1
Ohio Power Co [Member] | Excess ADIT [Member]
Decrease in Total Revenue		(1.4)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 1.4
Public Service Co Of Oklahoma [Member]
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ (1.3)	$ (22.3)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 5.7	$ (1.9)
Effective Income Tax Rate		16.30%	37.70%
Public Service Co Of Oklahoma [Member] | Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (3.8)
Increase in Current Liabilities		0.0
Increase in Deferred Credits and Other Noncurrent Liabilities		3.8
Public Service Co Of Oklahoma [Member] | Excess ADIT [Member]
Decrease in Total Revenue		(2.2)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 2.2
Southwestern Electric Power Co [Member]
Statutory Tax Rate on Pretax Income		21.00%	35.00%
Increase in Current Liabilities		$ (12.5)	$ (19.1)
Increase in Deferred Credits and Other Noncurrent Liabilities		$ 18.8	$ (12.1)
Effective Income Tax Rate		18.40%	37.30%
Southwestern Electric Power Co [Member] | Reduction in Corporate Federal Income Tax Rate [Member]
Decrease in Total Revenue		$ (11.0)
Increase in Current Liabilities		0.0
Increase in Deferred Credits and Other Noncurrent Liabilities		11.0
Southwestern Electric Power Co [Member] | Excess ADIT [Member]
Decrease in Total Revenue		(3.5)
Increase in Deferred Credits and Other Noncurrent Liabilities		3.5
Subsequent Event [Member]
Kentucky Single Corporate Tax Rate	5.00%
Subsequent Event [Member] | AEP Transmission Co [Member]
Kentucky Single Corporate Tax Rate	5.00%
Subsequent Event [Member] | Indiana Michigan Power Co [Member]
Kentucky Single Corporate Tax Rate	5.00%
Subsequent Event [Member] | Ohio Power Co [Member]
Kentucky Single Corporate Tax Rate	5.00%
Net Regulatory Liability for Tax Reform [Member]
Excess Accumulated Deferred Income Taxes		4,400.0
Incremental Liability for Tax Reform [Member]
Excess Accumulated Deferred Income Taxes		1,200.0
Pretax Excess ADIT [Member]
Excess Accumulated Deferred Income Taxes		4,400.0
Temporary Differences Associated with Depreciable Property [Member]
Excess Accumulated Deferred Income Taxes		3,400.0
Remaining Excess ADIT [Member]
Excess Accumulated Deferred Income Taxes		$ 1,000.0