Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	5.20%	(16.20%)	1.70%	5.60%
Income Tax Expense (Benefit)	$ (40.6)	$ 80.7	$ (30.7)	$ (93.5)
Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 71.0		$ (93.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	19.10%		(4.50%)
State Income Tax Expenses [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 14.0
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	1.30%
Kentucky Legislation - House Bill 487 [Member]
Kentucky Single Corporate Tax Rate				5.00%
Kentucky Legislation - House Bill 366 [Member]
Kentucky Net Operating Loss Limitation Percent				80.00%
Remeasurement of Kentucky Deferred Taxes [Member]
Income Tax Expense (Benefit)		$ 18.0
AEP Texas Inc. [Member]
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	15.10%	12.60%	(25.30%)	14.90%
Income Tax Expense (Benefit)	$ (13.7)	$ (8.3)	$ 38.8	$ (26.4)
AEP Texas Inc. [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount			$ (59.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent			(38.90%)
AEP Transmission Co [Member]
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	21.90%	18.40%	20.70%	20.70%
Income Tax Expense (Benefit)	$ (30.1)	$ (17.6)	$ (90.7)	$ (63.7)
AEP Transmission Co [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 2.0
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	1.00%
AEP Transmission Co [Member] | State Income Tax Expenses [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 3.0
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	1.30%
AEP Transmission Co [Member] | Kentucky Legislation - House Bill 487 [Member]
Kentucky Single Corporate Tax Rate				5.00%
AEP Transmission Co [Member] | Kentucky Legislation - House Bill 366 [Member]
Kentucky Net Operating Loss Limitation Percent				80.00%
Appalachian Power Co [Member]
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	(3.90%)	(962.20%)	(19.10%)	(13.80%)
Income Tax Expense (Benefit)	$ 3.9	$ 78.9	$ 47.0	$ 35.1
Appalachian Power Co [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 56.0		$ (9.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	947.30%		(4.60%)
Appalachian Power Co [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member] | West Virginia Tax Reform [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount		$ (73.0)
Appalachian Power Co [Member] | State Income Tax Expenses [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 6.0
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	34.80%
Indiana Michigan Power Co [Member]
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	(2.70%)	15.90%	(2.10%)	10.40%
Income Tax Expense (Benefit)	$ 2.3	$ (13.7)	$ 5.1	$ (26.8)
Indiana Michigan Power Co [Member] | Amortization of Excess ADIT [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ (10.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	(11.30%)		(6.90%)
Indiana Michigan Power Co [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount			$ (16.0)
Indiana Michigan Power Co [Member] | Flow-Through Items [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ (3.0)		$ (12.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	(3.20%)		(4.80%)
Indiana Michigan Power Co [Member] | State Income Tax Expenses [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 2.0
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	(1.80%)
Indiana Michigan Power Co [Member] | Parent Company Loss Benefit [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ (1.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	(1.60%)
Indiana Michigan Power Co [Member] | Kentucky Legislation - House Bill 487 [Member]
Kentucky Single Corporate Tax Rate				5.00%
Indiana Michigan Power Co [Member] | Kentucky Legislation - House Bill 366 [Member]
Kentucky Net Operating Loss Limitation Percent				80.00%
Ohio Power Co [Member]
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	13.90%	(46.40%)	14.20%	4.60%
Income Tax Expense (Benefit)	$ (11.2)	$ 28.1	$ (40.9)	$ (11.4)
Ohio Power Co [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 35.0		$ 24.0
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	60.00%		10.80%
Ohio Power Co [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member] | Ohio Tax Reform [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount		$ (38.0)		$ (38.0)
Ohio Power Co [Member] | Parent Company Loss Benefit [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ 1.0
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	2.00%
Ohio Power Co [Member] | Kentucky Legislation - House Bill 487 [Member]
Kentucky Single Corporate Tax Rate				5.00%
Ohio Power Co [Member] | Kentucky Legislation - House Bill 366 [Member]
Kentucky Net Operating Loss Limitation Percent				80.00%
Public Service Co Of Oklahoma [Member]
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	6.40%	5.60%	4.60%	8.70%
Income Tax Expense (Benefit)	$ (6.9)	$ (3.6)	$ (7.2)	$ (8.6)
Public Service Co Of Oklahoma [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount			$ (15.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent			(6.80%)
Southwestern Electric Power Co [Member]
Federal Statutory Income Tax Rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate	(0.60%)	9.80%	0.00%	11.40%
Income Tax Expense (Benefit)	$ 0.7	$ (9.6)	$ 0.0	$ (17.9)
Southwestern Electric Power Co [Member] | Amortization of Excess ADIT Not Subject to Normalization Requirements [Member]
Effective Income Tax Rate Reconciliation, Variance Explanation, Amount	$ (11.0)		$ (15.0)
Effective Income Tax Rate Reconciliation, Variance Explanation, Percent	(9.70%)		10.40%