Business Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021		Mar. 31, 2020		Dec. 31, 2020
Reportable Segment Information
Revenue from Contracts with Customers		$ 4,281.1		$ 3,747.5
Revenue from Related Parties		0.0		0.0
Revenues		4,281.1		3,747.5
Net Income (Loss)		578.8		499.3
Balance Sheet Information
Total Property, Plant and Equipment		85,612.9				$ 84,313.0
Accumulated Depreciation and Amortization		20,916.8				20,411.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		64,696.1				63,901.6
Total Assets		82,985.1				80,757.2
Long-term Debt Due Within One Year		2,130.2				2,086.1
Long-term Debt - Affiliated		0.0				0.0
Long-term Debt		30,214.8				28,986.4
Total Long-term Debt Outstanding		32,345.0				31,072.5
Income Tax (Expense) Benefit		54.5		46.5
Interest Expense		290.2		292.1
Reclassification out of Accumulated Other Comprehensive Income [Member]
Balance Sheet Information
Income Tax (Expense) Benefit		(36.1)		10.4
Interest Expense	[1]	1.5		0.9
Interest Rate [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Balance Sheet Information
Income Tax (Expense) Benefit		0.4		0.2
Interest Expense	[1]	1.5		0.9
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,504.5		2,193.0
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,082.3		1,075.2
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		601.7		408.4
Generation and Marketing Revenues [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[1]	0.8		(0.1)
Generation and Marketing Revenues [Member] | Interest Rate [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[1]	0.0		0.0
Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		92.6		70.9
Revenues		4.8	[2]	19.9	[3]
AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Related Parties		285.6		233.7
Revenues		361.7		295.6
Net Income (Loss)		151.7		117.8
Balance Sheet Information
Total Property, Plant and Equipment		11,694.0				11,345.6
Accumulated Depreciation and Amortization		623.6				572.8
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		11,070.4				10,772.8
Notes Receivable, Related Parties		0.0				0.0
Total Assets		11,515.1				11,246.0
Long-term Debt Due Within One Year		50.0				50.0
Long-term Debt		3,899.0				3,898.5
Total Long-term Debt Outstanding		3,949.0				3,948.5
Income Tax (Expense) Benefit		39.6		31.8
Interest Income		0.1		0.8
Interest Expense		34.1		29.6
AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.1		0.6
Revenues		0.0	[4]	0.0	[5]
AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		76.0		61.3
Reconciling Adjustments [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0
Revenue from Related Parties		(368.4)		(354.8)
Revenues		(368.4)		(354.8)
Net Income (Loss)		0.0		0.0
Balance Sheet Information
Total Property, Plant and Equipment		0.0				0.0
Accumulated Depreciation and Amortization		0.0				0.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		0.0				0.0
Total Assets	[6]	(4,562.7)				(3,961.7)
Long-term Debt Due Within One Year		0.0				0.0
Long-term Debt - Affiliated		(65.0)				(65.0)
Long-term Debt		0.0				0.0
Total Long-term Debt Outstanding		(65.0)				(65.0)
Reconciling Adjustments [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		(3.6)	[2]	(25.5)	[3]
Reconciling Adjustments [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0
Revenue from Related Parties		0.0		0.0
Revenues		0.0		0.0
Net Income (Loss)		0.0		0.0
Balance Sheet Information
Total Property, Plant and Equipment		0.0				0.0
Accumulated Depreciation and Amortization		0.0				0.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		0.0				0.0
Notes Receivable, Related Parties	[7]	(3,899.0)				(3,948.5)
Total Assets	[8]	(4,050.4)				(4,023.1)
Total Long-term Debt Outstanding	[7]	(3,990.0)				(3,990.0)
Income Tax (Expense) Benefit		0.0		0.0
Interest Income	[9]	(38.2)		(33.4)
Interest Expense	[9]	(38.2)		(33.4)
Reconciling Adjustments [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Related Parties		32.8		33.7
Revenues		2,537.3		2,226.7
Net Income (Loss)		271.4		246.3
Balance Sheet Information
Total Property, Plant and Equipment		49,448.9				49,023.3
Accumulated Depreciation and Amortization		15,950.1				15,586.2
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		33,498.8				33,437.1
Total Assets		44,591.3				42,752.7
Long-term Debt Due Within One Year		1,078.3				1,034.6
Long-term Debt - Affiliated		65.0				65.0
Long-term Debt		13,185.8				12,375.6
Total Long-term Debt Outstanding		14,329.1				13,475.2
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,504.5		2,193.0
Vertically Integrated Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		0.0	[2]	0.0	[3]
Transmission And Distribution Utilities [Member]
Reportable Segment Information
Revenue from Related Parties		5.8		31.7
Revenues		1,088.1		1,106.9
Net Income (Loss)		114.4		116.2
Balance Sheet Information
Total Property, Plant and Equipment		21,492.9				21,145.0
Accumulated Depreciation and Amortization		3,951.3				3,879.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		17,541.6				17,265.7
Total Assets		20,076.9				19,765.9
Long-term Debt Due Within One Year		589.0				588.8
Long-term Debt - Affiliated		0.0				0.0
Long-term Debt		7,097.4				6,661.9
Total Long-term Debt Outstanding		7,686.4				7,250.7
Transmission And Distribution Utilities [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,082.3		1,075.2
Transmission And Distribution Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		5.3	[2]	29.3	[3]
AEP Transmission Holdco [Member]
Reportable Segment Information
Revenue from Related Parties		289.1		237.1
Revenues		377.0		310.2
Net Income (Loss)		173.2		141.6
Balance Sheet Information
Total Property, Plant and Equipment		12,185.2				11,827.2
Accumulated Depreciation and Amortization		648.1				595.7
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		11,537.1				11,231.5
Total Assets		12,925.8				12,627.3
Long-term Debt Due Within One Year		52.4				52.3
Long-term Debt - Affiliated		0.0				0.0
Long-term Debt		4,089.7				4,075.7
Total Long-term Debt Outstanding		4,142.1				4,128.0
AEP Transmission Holdco [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		87.9		73.1
Generation And Marketing [Member]
Reportable Segment Information
Revenue from Related Parties		32.5		30.2
Revenues		634.2		438.6
Net Income (Loss)		38.2		30.5
Balance Sheet Information
Total Property, Plant and Equipment		2,080.6				1,910.2
Accumulated Depreciation and Amortization		183.8				166.1
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		1,896.8				1,744.1
Total Assets		3,881.8				3,585.9
Long-term Debt Due Within One Year		0.0				0.0
Long-term Debt - Affiliated		0.0				0.0
Long-term Debt		0.0				0.0
Total Long-term Debt Outstanding		0.0				0.0
Generation And Marketing [Member] | Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		601.7		408.4
Generation And Marketing [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		0.0	[2]	18.3	[3]
All Other [Member]
Reportable Segment Information
Revenue from Related Parties	[10]	8.2		22.1
Revenues	[10]	12.9		19.9
Net Income (Loss)	[10]	(18.4)		(35.3)
Balance Sheet Information
Total Property, Plant and Equipment	[10]	405.3				407.3
Accumulated Depreciation and Amortization	[10]	183.5				184.1
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[10]	221.8				223.2
Total Assets	[10],[11]	6,072.0				5,987.1
Long-term Debt Due Within One Year	[10],[12]	410.5				410.4
Long-term Debt - Affiliated	[10]	0.0				0.0
Long-term Debt	[10],[12]	5,841.9				5,873.2
Total Long-term Debt Outstanding	[10],[12]	6,252.4				6,283.6
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[10]	4.7		(2.2)
Revenues		3.1	[2]	(2.2)	[3]
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Related Parties		285.6		233.7
Revenues		361.7		295.6
Net Income (Loss)		151.7		117.3
Balance Sheet Information
Total Property, Plant and Equipment		11,694.0				11,345.6
Accumulated Depreciation and Amortization		623.6				572.8
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		11,070.4				10,772.8
Notes Receivable, Related Parties		0.0				0.0
Total Assets		11,458.3				11,185.1
Total Long-term Debt Outstanding		3,990.0				3,990.0
Income Tax (Expense) Benefit		39.6		31.8
Interest Income		0.0		0.2
Interest Expense		34.1		29.6
State Transcos [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.1		0.6
State Transcos [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		76.0		61.3
AEPTCo Parent [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0
Revenue from Related Parties		0.0		0.0
Revenues		0.0		0.0
Net Income (Loss)	[13]	0.0		0.5
Balance Sheet Information
Total Property, Plant and Equipment		0.0				0.0
Accumulated Depreciation and Amortization		0.0				0.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		0.0				0.0
Notes Receivable, Related Parties		3,899.0				3,948.5
Total Assets	[14]	4,107.2				4,084.0
Total Long-term Debt Outstanding		3,949.0				$ 3,948.5
Income Tax (Expense) Benefit		0.0		0.0
Interest Income		38.3		34.0
Interest Expense		$ 38.2		$ 33.4

[1] Amounts reclassified to the referenced line item on the statements of income.

[2] Amounts include affiliated and nonaffiliated revenues.

[3] Amounts include affiliated and nonaffiliated revenues

[4] Amounts include affiliated and nonaffiliated revenues.

[5] Amounts include affiliated and nonaffiliated revenues.

[6] Reconciling Adjustments for Total Assets primarily include elimination of intercompany advances to affiliates and intercompany accounts receivable.

[7] Elimination of intercompany debt.

[8] Primarily relates to the elimination of Notes Receivable from the State Transcos.

[9] Elimination of intercompany interest income/interest expense on affiliated debt arrangement.

[10] Corporate and Other primarily includes the purchasing of receivables from certain AEP utility subsidiaries. This segment also includes Parent’s guarantee revenue received from affiliates, investment income, interest income, interest expense and other nonallocated costs.

[11] Includes elimination of AEP Parent’s investments in wholly-owned subsidiary companies.

[12] Amounts are inclusive of the impact of fair value hedge accounting. See “Accounting for Fair Value Hedging Strategies” section of Note 10 for additional information.

[13] Includes the elimination of AEPTCo Parent’s equity earnings in the State Transcos.

[14] Includes the elimination of AEPTCo Parent’s investments in State Transcos.