Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Plans [Member]
Components of Net Periodic Benefit Cost
Service Cost	$ 23.8	$ 24.4	$ 71.6	$ 73.2
Interest Cost	51.1	46.9	153.3	140.8
Expected Return on Plan Assets	(74.0)	(72.6)	(222.0)	(217.7)
Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Amortization of Net Actuarial Loss	14.4	21.3	43.2	63.9
Net Periodic Benefit Cost (Credit)	15.3	20.0	46.1	60.2
Pension Plans [Member] | AEP Texas Inc. [Member]
Components of Net Periodic Benefit Cost
Service Cost	2.2	2.3	6.5	6.9
Interest Cost	4.4	4.0	13.1	12.0
Expected Return on Plan Assets	(6.5)	(6.4)	(19.4)	(19.2)
Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Amortization of Net Actuarial Loss	1.2	1.8	3.7	5.4
Net Periodic Benefit Cost (Credit)	1.3	1.7	3.9	5.1
Pension Plans [Member] | Appalachian Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	2.4	2.4	7.1	7.0
Interest Cost	6.3	5.8	18.9	17.6
Expected Return on Plan Assets	(9.4)	(9.1)	(28.1)	(27.4)
Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Amortization of Net Actuarial Loss	1.8	2.6	5.3	7.9
Net Periodic Benefit Cost (Credit)	1.1	1.7	3.2	5.1
Pension Plans [Member] | Indiana Michigan Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	3.3	3.4	10.0	10.2
Interest Cost	6.0	5.6	17.9	16.6
Expected Return on Plan Assets	(9.1)	(9.0)	(27.5)	(26.8)
Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Amortization of Net Actuarial Loss	1.6	2.5	4.9	7.4
Net Periodic Benefit Cost (Credit)	1.8	2.5	5.3	7.4
Pension Plans [Member] | Ohio Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	1.9	2.0	5.9	5.8
Interest Cost	4.8	4.4	14.3	13.3
Expected Return on Plan Assets	(7.3)	(7.2)	(22.0)	(21.6)
Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Amortization of Net Actuarial Loss	1.3	2.0	4.0	6.0
Net Periodic Benefit Cost (Credit)	0.7	1.2	2.2	3.5
Pension Plans [Member] | Public Service Co Of Oklahoma [Member]
Components of Net Periodic Benefit Cost
Service Cost	1.6	1.7	4.9	5.3
Interest Cost	2.6	2.5	7.9	7.4
Expected Return on Plan Assets	(4.0)	(4.0)	(12.2)	(12.1)
Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Amortization of Net Actuarial Loss	0.7	1.1	2.2	3.3
Net Periodic Benefit Cost (Credit)	0.9	1.3	2.8	3.9
Pension Plans [Member] | Southwestern Electric Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	2.1	2.4	6.4	7.0
Interest Cost	3.1	2.8	9.3	8.5
Expected Return on Plan Assets	(4.4)	(4.4)	(13.3)	(13.1)
Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Amortization of Net Actuarial Loss	0.9	1.3	2.6	3.8
Net Periodic Benefit Cost (Credit)	1.7	2.1	5.0	6.2
Other Postretirement Benefit Plans [Member]
Components of Net Periodic Benefit Cost
Service Cost	2.4	2.9	7.1	8.7
Interest Cost	12.6	11.8	37.9	35.5
Expected Return on Plan Assets	(23.4)	(25.6)	(70.3)	(76.7)
Amortization of Prior Service Cost (Credit)	(17.3)	(17.3)	(51.8)	(51.8)
Amortization of Net Actuarial Loss	5.5	2.7	16.6	7.9
Net Periodic Benefit Cost (Credit)	(20.2)	(25.5)	(60.5)	(76.4)
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member]
Components of Net Periodic Benefit Cost
Service Cost	0.1	0.3	0.5	0.7
Interest Cost	1.0	0.9	3.0	2.8
Expected Return on Plan Assets	(1.9)	(2.1)	(5.8)	(6.4)
Amortization of Prior Service Cost (Credit)	(1.5)	(1.5)	(4.4)	(4.4)
Amortization of Net Actuarial Loss	0.5	0.2	1.4	0.6
Net Periodic Benefit Cost (Credit)	(1.8)	(2.2)	(5.3)	(6.7)
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	0.2	0.3	0.7	0.8
Interest Cost	2.2	2.1	6.5	6.2
Expected Return on Plan Assets	(3.7)	(4.0)	(11.0)	(12.0)
Amortization of Prior Service Cost (Credit)	(2.5)	(2.5)	(7.5)	(7.5)
Amortization of Net Actuarial Loss	1.0	0.4	2.8	1.4
Net Periodic Benefit Cost (Credit)	(2.8)	(3.7)	(8.5)	(11.1)
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	0.3	0.4	1.0	1.2
Interest Cost	1.5	1.4	4.4	4.1
Expected Return on Plan Assets	(2.8)	(3.1)	(8.5)	(9.3)
Amortization of Prior Service Cost (Credit)	(2.4)	(2.4)	(7.1)	(7.1)
Amortization of Net Actuarial Loss	0.7	0.3	2.0	0.9
Net Periodic Benefit Cost (Credit)	(2.7)	(3.4)	(8.2)	(10.2)
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	0.2	0.2	0.6	0.7
Interest Cost	1.4	1.3	4.1	3.9
Expected Return on Plan Assets	(2.7)	(2.9)	(8.1)	(8.8)
Amortization of Prior Service Cost (Credit)	(1.8)	(1.7)	(5.2)	(5.2)
Amortization of Net Actuarial Loss	0.6	0.3	1.9	0.8
Net Periodic Benefit Cost (Credit)	(2.3)	(2.8)	(6.7)	(8.6)
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]
Components of Net Periodic Benefit Cost
Service Cost	0.2	0.1	0.5	0.5
Interest Cost	0.7	0.6	2.0	1.8
Expected Return on Plan Assets	(1.3)	(1.3)	(3.9)	(4.1)
Amortization of Prior Service Cost (Credit)	(1.1)	(1.1)	(3.2)	(3.2)
Amortization of Net Actuarial Loss	0.3	0.1	0.9	0.4
Net Periodic Benefit Cost (Credit)	(1.2)	(1.6)	(3.7)	(4.6)
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]
Components of Net Periodic Benefit Cost
Service Cost	0.2	0.2	0.6	0.7
Interest Cost	0.7	0.7	2.3	2.1
Expected Return on Plan Assets	(1.5)	(1.6)	(4.5)	(4.8)
Amortization of Prior Service Cost (Credit)	(1.3)	(1.3)	(3.9)	(3.9)
Amortization of Net Actuarial Loss	0.4	0.2	1.1	0.5
Net Periodic Benefit Cost (Credit)	$ (1.5)	$ (1.8)	$ (4.4)	$ (5.4)