CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN MEMBER’S EQUITY - AEP Transmission Holdco - USD ($) $ in Millions	Total	Paid-in Capital	Retained Earnings	Noncontrolling Interests	AEPTCo	AEPTCo Paid-in Capital	AEPTCo Retained Earnings	AEPTCo Noncontrolling Interests
Beginning balance at Dec. 31, 2023					$ 6,333.3	$ 3,043.4	$ 3,289.9	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Capital Contribution from AEP Member					25.0	25.0
Dividends Paid to AEP Member					(40.0)		(40.0)
Net Income	$ 1,005.7		$ 1,003.1	$ 2.6	181.2		181.2
Ending balance at Mar. 31, 2024					6,499.5	3,068.4	3,431.1	0.0
Beginning balance at Dec. 31, 2023					6,333.3	3,043.4	3,289.9	0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	2,309.9				548.2
Ending balance at Sep. 30, 2024					6,814.6	3,073.5	3,741.1	0.0
Beginning balance at Mar. 31, 2024					6,499.5	3,068.4	3,431.1	0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Capital Contribution from AEP Member					9.6	9.6
Dividends Paid to AEP Member					(31.0)		(31.0)
Net Income	342.5		340.3	2.2	175.7		175.7
Ending balance at Jun. 30, 2024					6,653.8	3,078.0	3,575.8	0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Return of Capital to Parent					(4.5)	(4.5)
Dividends Paid to AEP Member					(26.0)		(26.0)
Net Income	961.7		959.6	2.1	191.3		191.3
Ending balance at Sep. 30, 2024					6,814.6	3,073.5	3,741.1	0.0
Beginning balance at Dec. 31, 2024					6,950.9	3,100.6	3,850.3	0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Capital Contribution from AEP Member					32.5	32.5
Dividends Paid to AEP Member					(42.5)		(42.5)
Net Income	802.2		800.2	2.0	211.5		211.5
Ending balance at Mar. 31, 2025					7,152.4	3,133.1	4,019.3	0.0
Beginning balance at Dec. 31, 2024					6,950.9	3,100.6	3,850.3	0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	3,090.8				1,033.5
Ending balance at Sep. 30, 2025					7,713.0	4,934.0	1,733.9	1,045.1
Beginning balance at Mar. 31, 2025					7,152.4	3,133.1	4,019.3	0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Capital Contribution from AEP Member					8.3	8.3
Dividends Paid to AEP Member					(2,835.8)		(2,835.8)
Midwest Transmission Holdings Noncontrolling Interest Transaction	2,782.9	$ 1,790.5		992.4	2,782.9	1,790.5		992.4
Net Income	1,288.3		1,225.8	62.5	616.5		555.8	60.7
Ending balance at Jun. 30, 2025					7,724.3	4,931.9	1,739.3	1,053.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Capital Contribution from AEP Member					2.1	2.1
Capital Contribution from Noncontrolling Interest	33.9			33.9	33.9			33.9
Dividends Paid to AEP Member					(184.3)		(184.3)
Dividends Paid to Noncontrolling Interest	(69.5)			(69.5)	(68.5)			(68.5)
Net Income	$ 1,000.3		$ 972.0	$ 28.3	205.5		178.9	26.6
Ending balance at Sep. 30, 2025					$ 7,713.0	$ 4,934.0	$ 1,733.9	$ 1,045.1