Business Segments (Details) - USD ($) $ in Millions		3 Months Ended						6 Months Ended
		Jun. 30, 2020		Mar. 31, 2020	Jun. 30, 2019		Mar. 31, 2019	Jun. 30, 2020		Jun. 30, 2019		Dec. 31, 2019
Reportable Segment Information
Revenue from Contracts with Customers		$ 3,494.0			$ 3,573.6			$ 7,241.5		$ 7,630.4
Sales to AEP Affiliates		0.0			0.0			0.0		0.0
Total Revenues		3,494.0			3,573.6			7,241.5		7,630.4
Interest Expense		294.0			250.7			586.1		506.5
Income Tax Expense (Benefit)		12.6			(54.4)			59.1		(9.9)
Net Income (Loss)		514.5		$ 499.3	459.1		$ 574.1	1,013.8		1,033.2
Balance Sheet Information
Total Property, Plant and Equipment		81,704.2						81,704.2				$ 79,145.7
Accumulated Depreciation and Amortization		19,777.4						19,777.4				19,007.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		61,926.8						61,926.8				60,138.1
Total Assets		77,804.8						77,804.8				75,892.3
Affiliated Long Term Debt Current		0.0						0.0				0.0
Long-term Debt Due Within One Year		2,137.7						2,137.7				1,598.7
Long-term Debt - Affiliated		0.0						0.0				0.0
Long-term Debt		26,637.7						26,637.7				25,126.8
Total Long-term Debt Outstanding		28,775.4						28,775.4				26,725.5
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reportable Segment Information
Interest Expense	[1]	1.4			0.3			2.3		0.5
Income Tax Expense (Benefit)		10.6			4.2			21.0		6.4
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
Interest Expense	[1]	1.4			0.3			2.3		0.5
Income Tax Expense (Benefit)		0.4			0.1			0.6		0.1
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,062.3			2,116.4			4,255.3		4,488.7
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,009.4			1,001.6			2,084.6		2,181.4
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		350.2			382.9			758.6		822.6
Generation and Marketing Revenues [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[1]	(0.1)						(0.2)
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		72.1			72.7			143.0		137.7
Total Revenues		(1.1)	[2]		(9.4)	[3]		18.8	[4]	40.3	[5]
AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		177.7			209.1			411.4		402.3
Total Revenues		238.1			266.9			533.7		510.4
Interest Income		1.3			0.6			2.1		1.3
Interest Expense		32.8			21.4			62.4		43.1
Income Tax Expense (Benefit)		19.3			33.0			51.1		60.6
Net Income (Loss)		73.7		$ 117.8	136.0		$ 104.3	191.5		240.3
Balance Sheet Information
Total Property, Plant and Equipment		10,545.4						10,545.4				9,893.2
Accumulated Depreciation and Amortization		488.3						488.3				402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,057.1						10,057.1				9,490.9
Notes Receivable, Related Parties		0.0						0.0				0.0
Total Assets		10,475.7						10,475.7				9,890.8
Long-term Debt		3,947.4						3,947.4				3,427.3
Total Long-term Debt Outstanding		3,947.4						3,947.4				3,427.3
AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		60.4			57.8			121.7		108.1
AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0			0.0			0.6		0.0
Total Revenues		0.0	[6]		0.0	[7]		0.0	[8]	0.0	[9]
Reconciling Adjustments [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0			0.0			0.0		0.0
Sales to AEP Affiliates		(278.6)			(311.3)			(633.4)		(643.5)
Total Revenues		(278.6)			(311.3)			(633.4)		(643.5)
Net Income (Loss)		0.0			0.0			0.0		0.0
Balance Sheet Information
Total Property, Plant and Equipment	[10]	(354.5)						(354.5)				(354.5)
Accumulated Depreciation and Amortization	[10]	(186.6)						(186.6)				(186.4)
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[10]	(167.9)						(167.9)				(168.1)
Total Assets	[10],[11]	(4,346.8)						(4,346.8)				(3,801.3)
Affiliated Long Term Debt Current		(20.0)						(20.0)				(20.0)
Long-term Debt Due Within One Year		0.0						0.0				0.0
Long-term Debt - Affiliated		(39.0)						(39.0)				(39.0)
Long-term Debt		0.0						0.0				0.0
Total Long-term Debt Outstanding		(59.0)						(59.0)				(59.0)
Reconciling Adjustments [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		(10.8)	[2]		(69.4)	[3]		(36.3)	[4]	(69.4)	[5]
Reconciling Adjustments [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0			0.0			0.0		0.0
Sales to AEP Affiliates		0.0			0.0			0.0		0.0
Total Revenues		0.0			0.0			0.0		0.0
Interest Income	[12]	(38.3)			(28.6)			(71.7)		(56.5)
Interest Expense	[12]	(38.3)			(28.6)			(71.7)		(56.5)
Income Tax Expense (Benefit)		0.0			0.0			0.0		0.0
Net Income (Loss)		0.0			0.0			0.0		0.0
Balance Sheet Information
Total Property, Plant and Equipment		0.0						0.0				0.0
Accumulated Depreciation and Amortization		0.0						0.0				0.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		0.0						0.0				0.0
Notes Receivable, Related Parties	[13]	(3,947.4)						(3,947.4)				(3,427.3)
Total Assets	[14]	(4,023.2)						(4,023.2)				(3,493.3)
Total Long-term Debt Outstanding	[13]	(3,990.0)						(3,990.0)				(3,465.0)
Reconciling Adjustments [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers								0.0
Vertically Integrated Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		29.7			7.4			63.4		38.4
Total Revenues		2,092.0			2,123.8			4,318.7		4,527.1
Net Income (Loss)		256.3			178.8			502.6		482.4
Balance Sheet Information
Total Property, Plant and Equipment		48,233.4						48,233.4				47,323.7
Accumulated Depreciation and Amortization		15,130.5						15,130.5				14,580.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		33,102.9						33,102.9				32,743.3
Total Assets		41,991.2						41,991.2				41,228.8
Affiliated Long Term Debt Current		20.0						20.0				20.0
Long-term Debt Due Within One Year		1,390.8						1,390.8				704.7
Long-term Debt - Affiliated		39.0						39.0				39.0
Long-term Debt		12,007.4						12,007.4				12,162.0
Total Long-term Debt Outstanding		13,457.2						13,457.2				12,925.7
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,062.3			2,116.4			4,255.3		4,488.7
Vertically Integrated Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		0.0	[2]		0.0	[3]		0.0	[4]	0.0	[5]
Transmission And Distribution Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		25.1			44.1			56.8		86.3
Total Revenues		1,034.5			1,045.7			2,141.4		2,267.7
Net Income (Loss)		139.5			131.4			255.7		287.9
Balance Sheet Information
Total Property, Plant and Equipment		20,650.2						20,650.2				19,773.3
Accumulated Depreciation and Amortization		4,001.7						4,001.7				3,911.2
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		16,648.5						16,648.5				15,862.1
Total Assets		19,209.5						19,209.5				18,757.5
Affiliated Long Term Debt Current		0.0						0.0				0.0
Long-term Debt Due Within One Year		239.2						239.2				392.2
Long-term Debt - Affiliated		0.0						0.0				0.0
Long-term Debt		6,552.9						6,552.9				6,248.1
Total Long-term Debt Outstanding		6,792.1						6,792.1				6,640.3
Transmission And Distribution Utilities [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,009.4			1,001.6			2,084.6		2,181.4
Transmission And Distribution Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		12.6	[2]		39.0	[3]		41.9	[4]	78.4	[5]
AEP Transmission Holdco [Member]
Reportable Segment Information
Sales to AEP Affiliates		180.5			209.1			417.6		404.3
Total Revenues		249.7			278.9			559.9		535.3
Net Income (Loss)		92.2			155.4			233.8		280.6
Balance Sheet Information
Total Property, Plant and Equipment		10,994.4						10,994.4				10,334.0
Accumulated Depreciation and Amortization		508.2						508.2				418.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,486.2						10,486.2				9,915.1
Total Assets		11,804.0						11,804.0				11,143.5
Affiliated Long Term Debt Current		0.0						0.0				0.0
Long-term Debt Due Within One Year		0.0						0.0				0.0
Long-term Debt - Affiliated		0.0						0.0				0.0
Long-term Debt		4,121.9						4,121.9				3,593.8
Total Long-term Debt Outstanding		4,121.9						4,121.9				3,593.8
AEP Transmission Holdco [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		69.2			69.8			142.3		131.0
Generation And Marketing [Member]
Reportable Segment Information
Sales to AEP Affiliates		26.7			29.8			56.9		71.9
Total Revenues		376.9			412.7			815.5		894.5
Net Income (Loss)		58.5			5.2			89.0		44.4
Balance Sheet Information
Total Property, Plant and Equipment		1,772.1						1,772.1				1,650.8
Accumulated Depreciation and Amortization		134.7						134.7				99.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		1,637.4						1,637.4				1,551.8
Total Assets		3,249.0						3,249.0				3,123.8
Affiliated Long Term Debt Current		0.0						0.0				0.0
Long-term Debt Due Within One Year		0.0						0.0				0.0
Long-term Debt - Affiliated		0.0						0.0				0.0
Long-term Debt		0.0						0.0				0.0
Total Long-term Debt Outstanding		0.0						0.0				0.0
Generation And Marketing [Member] | Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		350.2			382.9			758.6		822.6
Generation And Marketing [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		(0.6)	[2]		18.7	[3]		17.7	[4]	26.8	[5]
All Other [Member]
Reportable Segment Information
Sales to AEP Affiliates	[15]	16.6			20.9			38.7		42.6
Total Revenues	[15]	19.5			23.8			39.4		49.3
Net Income (Loss)	[15]	(32.0)			(11.7)			(67.3)		(62.1)
Balance Sheet Information
Total Property, Plant and Equipment	[15]	408.6						408.6				418.4
Accumulated Depreciation and Amortization	[15]	188.9						188.9				184.5
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[15]	219.7						219.7				233.9
Total Assets	[15],[16]	5,897.9						5,897.9				5,440.0
Affiliated Long Term Debt Current	[15]	0.0						0.0				0.0
Long-term Debt Due Within One Year	[15],[17]	507.7						507.7				501.8
Long-term Debt - Affiliated	[15]	0.0						0.0				0.0
Long-term Debt	[15],[17]	3,955.5						3,955.5				3,122.9
Total Long-term Debt Outstanding	[15]	4,463.2						4,463.2				3,624.7
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[15]	2.9			2.9			0.7		6.7
Total Revenues		(2.3)	[2]		2.3	[3]		(4.5)	[4]	4.5	[5]
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		177.7			209.1			411.4		402.3
Total Revenues		238.1			266.9			533.7		510.4
Interest Income		0.7			0.2			0.9		0.4
Interest Expense		32.8			21.4			62.4		43.1
Income Tax Expense (Benefit)		19.2			32.9			51.0		60.5
Net Income (Loss)		73.2			135.6			190.5		239.8
Balance Sheet Information
Total Property, Plant and Equipment		10,545.4						10,545.4				9,893.2
Accumulated Depreciation and Amortization		488.3						488.3				402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,057.1						10,057.1				9,490.9
Notes Receivable, Related Parties		0.0						0.0				0.0
Total Assets		10,434.6						10,434.6				9,865.0
Total Long-term Debt Outstanding		3,990.0						3,990.0				3,465.0
State Transcos [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		60.4			57.8			121.7		108.1
State Transcos [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers								0.6
AEPTCo Parent [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0			0.0			0.0		0.0
Sales to AEP Affiliates		0.0			0.0			0.0		0.0
Total Revenues		0.0			0.0			0.0		0.0
Interest Income		38.9			29.0			72.9		57.4
Interest Expense		38.3			28.6			71.7		56.5
Income Tax Expense (Benefit)		0.1			0.1			0.1		0.1
Net Income (Loss)	[18]	0.5			$ 0.4			1.0		$ 0.5
Balance Sheet Information
Total Property, Plant and Equipment		0.0						0.0				0.0
Accumulated Depreciation and Amortization		0.0						0.0				0.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		0.0						0.0				0.0
Notes Receivable, Related Parties		3,947.4						3,947.4				3,427.3
Total Assets	[19]	4,064.3						4,064.3				3,519.1
Total Long-term Debt Outstanding		$ 3,947.4						$ 3,947.4				$ 3,427.3

[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] Amounts include affiliated and nonaffiliated revenues.

[7] Amounts include affiliated and nonaffiliated revenues.

[8] Amounts include affiliated and nonaffiliated revenues.

[9] Amounts include affiliated and nonaffiliated revenues.

[10] Includes eliminations due to an intercompany finance lease.

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

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

[13] Elimination of intercompany debt.

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

[15] 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.

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

[17] 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

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

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