Property, Plant and Equipment (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
Asset Retirement Obligations (ARO)
Beginning Balance	[1],[2],[3],[4]	$ 2,516.7
Accretion Expense	[1],[2],[3],[4]	77.6
Liabilities Incurred	[1],[2],[3],[4]	17.7
Liabilities Settled	[1],[2],[3],[4]	(27.6)
Asset Retirement Obligation, Revision of Estimate	[1],[2],[3],[4]	75.1
Ending Balance	[1],[2],[3],[4]	2,659.5	$ 2,516.7
Appalachian Power Co [Member]
Asset Retirement Obligations (ARO)
Beginning Balance	[2],[3]	313.1
Accretion Expense	[2],[3]	9.9
Liabilities Incurred	[2],[3]	0.0
Liabilities Settled	[2],[3]	(5.8)
Asset Retirement Obligation, Revision of Estimate	[2],[3]	84.7
Ending Balance	[2],[3]	401.9	313.1
Indiana Michigan Power Co [Member]
Property, Plant and Equipment (Textuals)
Asset Retirement Obligations (ARO) Liability for Nuclear Decommissioning of the Cook Plant		1,850.0	1,800.0
Glen Lyn Station [Member] | Appalachian Power Co [Member]
Asset Retirement Obligations (ARO)
Asset Retirement Obligation, Revision of Estimate		$ 79.0	$ 199.0

[1] Includes ARO related to Sabine and DHLC.

[2] Includes ARO related to asbestos removal.

[3] Includes ARO related to ash disposal facilities.

[4] Includes ARO related to nuclear decommissioning costs for the Cook Plant of $1.85 billion and $1.80 billion as of September 30, 2021 and December 31, 2020, respectively.