Business Segments (Details) - USD ($) $ in Millions		3 Months Ended								9 Months Ended
		Sep. 30, 2020		Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019		Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020		Sep. 30, 2019		Dec. 31, 2019
Reportable Segment Information
Revenue from Contracts with Customers		$ 4,066.4				$ 4,315.0				$ 11,307.9		$ 11,945.4
Sales to AEP Affiliates		0.0				0.0				0.0		0.0
Total Revenues		4,066.4				4,315.0				11,307.9		11,945.4
Interest Expense		291.3				275.1				877.4		781.6
Income Tax Expense (Benefit)		(1.2)				40.6				57.9		30.7
Net Income (Loss)		748.2		$ 514.5	$ 499.3	733.9		$ 459.1	$ 574.1	1,762.0		1,767.1
Balance Sheet Information
Total Property, Plant and Equipment		82,903.0								82,903.0				$ 79,145.7
Accumulated Depreciation and Amortization		20,116.6								20,116.6				19,007.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		62,786.4								62,786.4				60,138.1
Total Assets		78,689.3								78,689.3				75,892.3
Affiliated Long-term Debt Due Within One Year														0.0
Long-term Debt Due Within One Year		1,911.6								1,911.6				1,598.7
Long-term Debt - Affiliated		0.0								0.0				0.0
Long-term Debt		28,155.5								28,155.5				25,126.8
Total Long-term Debt Outstanding		30,067.1								30,067.1				26,725.5
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reportable Segment Information
Interest Expense	[1]	1.3								3.6		0.5
Income Tax Expense (Benefit)		6.8				1.4				27.8		7.8
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]	1.3								3.6		0.5
Income Tax Expense (Benefit)		0.2				0.0				0.8		0.1
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,400.1				2,598.9				6,655.4		7,087.6
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,124.1				1,147.3				3,208.7		3,328.7
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		464.8				501.2				1,223.4		1,323.8
Generation and Marketing Revenues [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reportable Segment Information
Revenue from Contracts with Customers		(0.1)	[1]			(0.1)				(0.3)	[1]	(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		0.0	[1]			0.0				0.0	[1]	0.0
Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		77.4				67.6				220.4		205.3
Total Revenues		(5.5)	[2]			14.3	[3]			13.3	[4]	54.6	[5]
AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		241.2				205.7				652.6		608.0
Total Revenues		304.1				259.7				837.8		770.1
Interest Income		0.2				0.8				2.3		2.1
Interest Expense		32.7				26.4				95.1		69.5
Income Tax Expense (Benefit)		31.7				30.1				82.8		90.7
Net Income (Loss)		117.6		$ 73.7	$ 117.8	107.6		$ 136.0	$ 104.3	309.1		347.9
Balance Sheet Information
Total Property, Plant and Equipment		10,921.3								10,921.3				9,893.2
Accumulated Depreciation and Amortization		531.8								531.8				402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,389.5								10,389.5				9,490.9
Notes Receivable, Related Parties		0.0								0.0				0.0
Total Assets		10,698.7								10,698.7				9,890.8
Long-term Debt		3,947.9								3,947.9				3,427.3
Total Long-term Debt Outstanding		3,947.9								3,947.9				3,427.3
AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		62.9				54.0				184.6		162.1
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		(374.2)				(348.2)				(1,007.6)		(991.7)
Total Revenues		(374.2)				(348.2)				(1,007.6)		(991.7)
Net Income (Loss)		0.0				0.0				0.0		0.0
Balance Sheet Information
Total Property, Plant and Equipment		0.0								0.0				(354.5)	[10]
Accumulated Depreciation and Amortization		0.0								0.0				(186.4)	[10]
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		0.0								0.0				(168.1)	[10]
Total Assets	[11]	(3,794.7)								(3,794.7)				(3,801.3)	[10]
Affiliated Long-term Debt Due Within One Year														(20.0)
Long-term Debt Due Within One Year		0.0								0.0				0.0
Long-term Debt - Affiliated		(59.0)								(59.0)				(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		(35.0)	[2]			(39.8)	[3]			(71.3)	[4]	(109.2)	[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]	(38.2)				(31.9)				(109.9)		(88.4)
Interest Expense	[12]	(38.2)				(31.9)				(109.9)		(88.4)
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]	(3,947.9)								(3,947.9)				(3,427.3)
Total Assets	[14]	(4,047.2)								(4,047.2)				(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		34.7				46.6				98.1		85.0
Total Revenues		2,434.8				2,645.5				6,753.5		7,172.6
Net Income (Loss)		394.2				438.4				896.8		920.8
Balance Sheet Information
Total Property, Plant and Equipment		48,533.5								48,533.5				47,323.7
Accumulated Depreciation and Amortization		15,340.1								15,340.1				14,580.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		33,193.4								33,193.4				32,743.3
Total Assets		42,110.4								42,110.4				41,228.8
Affiliated Long-term Debt Due Within One Year														20.0
Long-term Debt Due Within One Year		1,313.7								1,313.7				704.7
Long-term Debt - Affiliated		59.0								59.0				39.0
Long-term Debt		12,048.7								12,048.7				12,162.0
Total Long-term Debt Outstanding		13,421.4								13,421.4				12,925.7
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,400.1				2,598.9				6,655.4		7,087.6
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		41.2				39.3				98.0		125.6
Total Revenues		1,165.3				1,186.6				3,306.7		3,454.3
Net Income (Loss)		147.4				133.7				403.1		421.6
Balance Sheet Information
Total Property, Plant and Equipment		20,738.7								20,738.7				19,773.3
Accumulated Depreciation and Amortization		3,891.6								3,891.6				3,911.2
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		16,847.1								16,847.1				15,862.1
Total Assets		19,250.3								19,250.3				18,757.5
Affiliated Long-term Debt Due Within One Year														0.0
Long-term Debt Due Within One Year		87.8								87.8				392.2
Long-term Debt - Affiliated		0.0								0.0				0.0
Long-term Debt		7,196.7								7,196.7				6,248.1
Total Long-term Debt Outstanding		7,284.5								7,284.5				6,640.3
Transmission And Distribution Utilities [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,124.1				1,147.3				3,208.7		3,328.7
Transmission And Distribution Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		36.2	[2]			38.9	[3]			78.1	[4]	117.3	[5]
AEP Transmission Holdco [Member]
Reportable Segment Information
Sales to AEP Affiliates		244.5				207.5				662.1		611.8
Total Revenues		317.9				273.0				877.8		808.3
Net Income (Loss)		139.3				127.0				373.1		407.6
Balance Sheet Information
Total Property, Plant and Equipment		11,377.1								11,377.1				10,334.0
Accumulated Depreciation and Amortization		553.1								553.1				418.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,824.0								10,824.0				9,915.1
Total Assets		12,035.8								12,035.8				11,143.5
Affiliated Long-term Debt Due Within One Year														0.0
Long-term Debt Due Within One Year		2.3								2.3				0.0
Long-term Debt - Affiliated		0.0								0.0				0.0
Long-term Debt		4,123.2								4,123.2				3,593.8
Total Long-term Debt Outstanding		4,125.5								4,125.5				3,593.8
AEP Transmission Holdco [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		73.4				65.5				215.7		196.5
Generation And Marketing [Member]
Reportable Segment Information
Sales to AEP Affiliates		25.2				32.5				82.1		104.4
Total Revenues		490.0				533.7				1,305.5		1,428.2
Net Income (Loss)		114.6				88.7				203.6		133.1
Balance Sheet Information
Total Property, Plant and Equipment		1,854.4								1,854.4				1,650.8
Accumulated Depreciation and Amortization		150.1								150.1				99.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		1,704.3								1,704.3				1,551.8
Total Assets		3,368.6								3,368.6				3,123.8
Affiliated Long-term Debt Due Within One Year														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		464.8				501.2				1,223.4		1,323.8
Generation And Marketing [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		(4.5)	[2]			26.4	[3]			13.2	[4]	53.2	[5]
All Other [Member]
Reportable Segment Information
Sales to AEP Affiliates	[15]	28.6				22.3				67.3		64.9
Total Revenues	[15]	32.6				24.4				72.0		73.7
Net Income (Loss)	[15]	(47.3)				(53.9)				(114.6)		(116.0)
Balance Sheet Information
Total Property, Plant and Equipment	[15]	399.3								399.3				418.4
Accumulated Depreciation and Amortization	[15]	181.7								181.7				184.5
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[15]	217.6								217.6				233.9
Total Assets	[15],[16]	5,718.9								5,718.9				5,440.0
Affiliated Long-term Debt Due Within One Year	[15]													0.0
Long-term Debt Due Within One Year	[15],[17]	507.8								507.8				501.8
Long-term Debt - Affiliated	[15]	0.0								0.0				0.0
Long-term Debt	[15],[17]	4,786.9								4,786.9				3,122.9
Total Long-term Debt Outstanding	[15]	5,294.7								5,294.7				3,624.7
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[15]	4.0				2.1				4.7		8.8
Total Revenues		(2.2)	[2]			(11.2)	[3]			(6.7)	[4]	(6.7)	[5]
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		241.2				205.7				652.6		608.0
Total Revenues		304.1				259.7				837.8		770.1
Interest Income		0.0				0.4				0.9		0.8
Interest Expense		32.7				26.4				95.1		69.5
Income Tax Expense (Benefit)		31.7				30.0				82.7		90.5
Net Income (Loss)		117.5				107.3				308.0		347.1
Balance Sheet Information
Total Property, Plant and Equipment		10,921.3								10,921.3				9,893.2
Accumulated Depreciation and Amortization		531.8								531.8				402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,389.5								10,389.5				9,490.9
Notes Receivable, Related Parties		0.0								0.0				0.0
Total Assets		10,641.8								10,641.8				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		62.9				54.0				184.6		162.1
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		38.4				32.3				111.3		89.7
Interest Expense		38.2				31.9				109.9		88.4
Income Tax Expense (Benefit)		0.0				0.1				0.1		0.2
Net Income (Loss)	[18]	0.1				$ 0.3				1.1		$ 0.8
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		3,947.9								3,947.9				3,427.3
Total Assets	[19]	4,104.1								4,104.1				3,519.1
Total Long-term Debt Outstanding		$ 3,947.9								$ 3,947.9				$ 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.