Income Taxes (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Income Tax Expense (Benefit)		$ 80.7		$ (264.0)		$ (93.5)		$ (797.8)
Increase in Current Liabilities						101.1		(260.3)
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 141.9		$ 205.7
Effective Income Tax Rate		(16.20%)		33.00%		5.60%		35.30%
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						$ 4,300.0
Incremental Liability for Tax Reform [Member]
Income Taxes (Textuals)
Excess Accumulated Deferred Income Taxes						1,100.0
Pretax Excess ADIT [Member]
Income Taxes (Textuals)
Excess Accumulated Deferred Income Taxes						4,300.0
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						900.0
AEP Texas Inc. [Member]
Income Tax Expense (Benefit)		$ (8.3)		$ (30.6)		(26.4)		$ (74.2)
Increase in Current Liabilities						14.1		(31.2)
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 67.1		$ 7.4
Effective Income Tax Rate		12.60%		32.20%		14.90%		33.60%
Income Taxes (Textuals)
Federal Statutory Income Tax Rate		21.00%		35.00%		21.00%		35.00%
AEP Transmission Co [Member]
Income Tax Expense (Benefit)		$ (17.6)		$ (29.5)	[1]	$ (63.7)	[1]	$ (108.2)	[1]
Increase in Current Liabilities						(28.0)		0.5
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 18.0		$ 25.7
Effective Income Tax Rate	[2]	18.40%		33.50%		20.70%		33.80%
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)		$ 78.9		$ (43.2)		$ 35.1		$ (136.7)
Increase in Current Liabilities						64.1		9.1
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 3.8		$ 7.9
Effective Income Tax Rate		(962.20%)		33.40%		(13.80%)		35.50%
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)		$ (13.7)		$ (28.6)		$ (26.8)		$ (61.8)
Increase in Current Liabilities						0.3		(14.2)
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 46.3		$ 40.9
Effective Income Tax Rate		15.90%		30.60%		10.40%		30.10%
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)		$ 28.1		$ (48.3)		$ (11.4)		$ (128.0)
Increase in Current Liabilities						(4.3)		(34.8)
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 62.5		$ 43.4
Effective Income Tax Rate		(46.40%)		36.90%		4.60%		35.60%
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%
Public Service Co Of Oklahoma [Member]
Income Tax Expense (Benefit)		$ (3.6)		$ (27.4)		$ (8.6)		$ (42.6)
Increase in Current Liabilities						15.1		1.5
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 10.9		$ (1.4)
Effective Income Tax Rate		5.60%		37.20%		8.70%		37.40%
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)		$ (9.6)		$ (22.5)		$ (17.9)		$ (45.2)
Increase in Current Liabilities						15.6		(14.6)
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 52.1		$ (5.2)
Effective Income Tax Rate		9.80%		21.20%		11.40%		25.70%
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						$ 51.1
Increase in Deferred Credits and Other Noncurrent Liabilities						98.4
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						21.9
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						8.6
Reduction in Corporate Federal Income Tax Rate [Member] | Appalachian Power Co [Member]
Increase in Current Liabilities						40.5
Increase in Deferred Credits and Other Noncurrent Liabilities						3.7
Reduction in Corporate Federal Income Tax Rate [Member] | Indiana Michigan Power Co [Member]
Increase in Current Liabilities						2.0
Increase in Deferred Credits and Other Noncurrent Liabilities						12.8
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						20.8
Reduction in Corporate Federal Income Tax Rate [Member] | Public Service Co Of Oklahoma [Member]
Increase in Current Liabilities						2.4
Increase in Deferred Credits and Other Noncurrent Liabilities						2.3
Reduction in Corporate Federal Income Tax Rate [Member] | Southwestern Electric Power Co [Member]
Increase in Current Liabilities						5.3
Increase in Deferred Credits and Other Noncurrent Liabilities						27.6
Excess ADIT [Member]
Increase in Current Liabilities						15.3
Increase in Deferred Credits and Other Noncurrent Liabilities						20.6
Excess ADIT [Member] | AEP Texas Inc. [Member]
Increase in Current Liabilities						0.0
Increase in Deferred Credits and Other Noncurrent Liabilities						6.9
Excess ADIT [Member] | AEP Transmission Co [Member]
Increase in Current Liabilities						0.0
Increase in Deferred Credits and Other Noncurrent Liabilities						0.1
Excess ADIT [Member] | Appalachian Power Co [Member]
Increase in Current Liabilities						9.5
Increase in Deferred Credits and Other Noncurrent Liabilities						0.7
Excess ADIT [Member] | Indiana Michigan Power Co [Member]
Increase in Current Liabilities						0.0
Increase in Deferred Credits and Other Noncurrent Liabilities						1.4
Excess ADIT [Member] | Ohio Power Co [Member]
Increase in Current Liabilities						0.0
Increase in Deferred Credits and Other Noncurrent Liabilities						3.3
Excess ADIT [Member] | Public Service Co Of Oklahoma [Member]
Increase in Current Liabilities						4.7
Increase in Deferred Credits and Other Noncurrent Liabilities						0.0
Excess ADIT [Member] | Southwestern Electric Power Co [Member]
Increase in Current Liabilities						1.2
Increase in Deferred Credits and Other Noncurrent Liabilities						$ 7.8
Amortization of Excess ADIT [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(7.40%)				(4.70%)
Amortization of Excess ADIT [Member] | Appalachian Power Co [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(31.70%)				(4.90%)
Amortization of Excess ADIT [Member] | Ohio Power Co [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(4.10%)				(2.50%)
Amortization of Excess ADIT [Member] | Public Service Co Of Oklahoma [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(17.30%)				(13.90%)
Amortization of Excess ADIT [Member] | Southwestern Electric Power Co [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(9.00%)				(7.90%)
Kentucky Legislation - House Bill 487 [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent						(1.10%)
IRS Audit Settlement [Member]
Reversed Unrecognized Tax Benefit			$ 72.0
Remeasurement of Kentucky Deferred Taxes [Member]
Income Tax Expense (Benefit)			$ 18.0
West Virginia Tax Reform [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(17.90%)				(5.40%)
West Virginia Tax Reform [Member] | Appalachian Power Co [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(887.80%)				(28.60%)
Ohio Tax Reform [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(7.80%)				(2.30%)
Ohio Tax Reform [Member] | Ohio Power Co [Member]
Income Taxes (Textuals)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent		(62.00%)				(15.10%)

[1] The amounts presented reflect the revisions made to AEPTCo’s previously issued financial statements. For additional details on revisions made to AEPTCo’s financial statements, see Note 1- Significant Accounting Matters.

[2] The 2017 ETRs presented above reflect the revisions made to AEPTCo's previously issued financial statements. See Note 1 - Significant Accounting Matters for additional information.