Business Segments (Details) - USD ($) $ in Millions		3 Months Ended								9 Months Ended
		Sep. 30, 2021		Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020		Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021		Sep. 30, 2020		Dec. 31, 2020
Reportable Segment Information
Revenue from Contracts with Customers		$ 4,623.0				$ 4,066.4				$ 12,730.6		$ 11,307.9
Revenue from Related Parties		0.0				0.0				0.0		0.0
Revenues		4,623.0				4,066.4				12,730.6		11,307.9
Net Income (Loss)		796.9		$ 573.8	$ 578.8	748.2		$ 514.5	$ 499.3	1,949.5		1,762.0
Balance Sheet Information
Total Property, Plant and Equipment		88,568.2								88,568.2				$ 84,313.0
Accumulated Depreciation and Amortization		21,877.0								21,877.0				20,411.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		66,691.2								66,691.2				63,901.6
Total Assets		86,337.1								86,337.1				80,757.2
Long-term Debt Due Within One Year		2,521.8								2,521.8				2,086.1
Long-term Debt - Affiliated		0.0								0.0				0.0
Long-term Debt		32,056.5								32,056.5				28,986.4
Total Long-term Debt Outstanding		34,578.3								34,578.3				31,072.5
Income Tax (Expense) Benefit		69.8				(1.2)				185.5		57.9
Interest Expense		303.7				291.3				895.5		877.4
Reclassification out of Accumulated Other Comprehensive Income [Member]
Balance Sheet Information
Income Tax (Expense) Benefit		(12.7)				6.8				(51.1)		27.8
Interest Expense	[1]	1.5				1.3				4.8		3.6
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		0.3				0.2				1.0		0.8
Interest Expense	[1]	1.5				1.3				4.8		3.6
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,716.8				2,400.1				7,445.9		6,655.4
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,195.0				1,124.1				3,366.9		3,208.7
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		617.4				464.8				1,641.6		1,223.4
Generation and Marketing Revenues [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[1]					(0.1)				0.7		(0.3)
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		0.0
Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		93.8				77.4				276.2		220.4
Revenues		154.8	[2]			(5.5)	[3]			188.7	[4]	13.3	[5]
AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Related Parties		297.6				241.2				864.6		652.6
Revenues		377.0				304.1				1,104.2		837.8
Net Income (Loss)		145.4		$ 148.6	$ 151.7	117.6		$ 73.7	$ 117.8	445.7		309.1
Balance Sheet Information
Total Property, Plant and Equipment		12,359.3								12,359.3				11,345.6
Accumulated Depreciation and Amortization		730.4								730.4				572.8
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		11,628.9								11,628.9				10,772.8
Notes Receivable, Related Parties		0.0								0.0				0.0
Total Assets		11,931.1								11,931.1				11,246.0
Long-term Debt Due Within One Year		50.0								50.0				50.0
Long-term Debt		4,343.4								4,343.4				3,898.5
Total Long-term Debt Outstanding		4,393.4								4,393.4				3,948.5
Income Tax (Expense) Benefit		36.7				31.7				115.4		82.8
Interest Income		0.2				0.2				0.4		2.3
Interest Expense		36.1				32.7				104.5		95.1
AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.2				0.0				0.3		0.6
Revenues		0.0	[6]			0.0	[7]			0.0	[8]	0.0	[9]
AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		79.2				62.9				239.3		184.6
Reconciling Adjustments [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0				0.0				0.0		0.0
Revenue from Related Parties		(376.0)				(374.2)				(1,112.2)		(1,007.6)
Revenues		(376.0)				(374.2)				(1,112.2)		(1,007.6)
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
Total Assets	[10]	(4,588.1)								(4,588.1)				(3,961.7)
Long-term Debt Due Within One Year		0.0								0.0				0.0
Long-term Debt - Affiliated		(65.0)								(65.0)				(65.0)
Long-term Debt		0.0								0.0				0.0
Total Long-term Debt Outstanding		(65.0)								(65.0)				(65.0)
Reconciling Adjustments [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		(3.0)	[2]			(35.0)	[3]			(8.6)	[4]	(71.3)	[5]
Reconciling Adjustments [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0				0.0				0.0		0.0
Revenue from Related Parties		0.0				0.0				0.0		0.0
Revenues		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	[11]	(4,343.5)								(4,343.5)				(3,948.5)
Total Assets	[12]	(4,498.9)								(4,498.9)				(4,023.1)
Total Long-term Debt Outstanding	[11]	(4,440.0)								(4,440.0)				(3,990.0)
Income Tax (Expense) Benefit		0.0				0.0				0.0		0.0
Interest Income	[13]	(40.2)				(38.2)				(116.7)		(109.9)
Interest Expense	[13]	(40.2)				(38.2)				(116.6)		(109.9)
Reconciling Adjustments [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0								0.0		0.0
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Related Parties		42.5				34.7				111.3		98.1
Revenues		2,759.3				2,434.8				7,557.2		6,753.5
Net Income (Loss)		438.7				394.2				938.9		896.8
Balance Sheet Information
Total Property, Plant and Equipment		50,990.6								50,990.6				49,023.3
Accumulated Depreciation and Amortization		16,647.1								16,647.1				15,586.2
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		34,343.5								34,343.5				33,437.1
Total Assets		45,775.5								45,775.5				42,752.7
Long-term Debt Due Within One Year		1,243.0								1,243.0				1,034.6
Long-term Debt - Affiliated		65.0								65.0				65.0
Long-term Debt		13,616.0								13,616.0				12,375.6
Total Long-term Debt Outstanding		14,924.0								14,924.0				13,475.2
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,716.8				2,400.1				7,445.9		6,655.4
Vertically Integrated Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		(0.9)	[2]			0.0	[3]			(0.6)	[4]	0.0	[5]
Transmission And Distribution Utilities [Member]
Reportable Segment Information
Revenue from Related Parties		5.3				41.2				24.9		98.0
Revenues		1,200.3				1,165.3				3,391.8		3,306.7
Net Income (Loss)		155.9				147.4				424.0		403.1
Balance Sheet Information
Total Property, Plant and Equipment		22,171.7								22,171.7				21,145.0
Accumulated Depreciation and Amortization		4,059.9								4,059.9				3,879.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		18,111.8								18,111.8				17,265.7
Total Assets		21,053.1								21,053.1				19,765.9
Long-term Debt Due Within One Year		815.2								815.2				588.8
Long-term Debt - Affiliated		0.0								0.0				0.0
Long-term Debt		7,869.0								7,869.0				6,661.9
Total Long-term Debt Outstanding		8,684.2								8,684.2				7,250.7
Transmission And Distribution Utilities [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,195.0				1,124.1				3,366.9		3,208.7
Transmission And Distribution Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		4.9	[2]			36.2	[3]			14.2	[4]	78.1	[5]
AEP Transmission Holdco [Member]
Reportable Segment Information
Revenue from Related Parties		301.3				244.5				882.2		662.1
Revenues		391.6				317.9				1,146.8		877.8
Net Income (Loss)		167.9				139.3				510.7		373.1
Balance Sheet Information
Total Property, Plant and Equipment		12,865.6								12,865.6				11,827.2
Accumulated Depreciation and Amortization		758.1								758.1				595.7
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		12,107.5								12,107.5				11,231.5
Total Assets		13,287.6								13,287.6				12,627.3
Long-term Debt Due Within One Year		52.4								52.4				52.3
Long-term Debt - Affiliated		0.0								0.0				0.0
Long-term Debt		4,544.2								4,544.2				4,075.7
Total Long-term Debt Outstanding		4,596.6								4,596.6				4,128.0
AEP Transmission Holdco [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		90.3				73.4				264.6		215.7
Generation And Marketing [Member]
Reportable Segment Information
Revenue from Related Parties		3.7				25.2				50.3		82.1
Revenues		621.1				490.0				1,691.9		1,305.5
Net Income (Loss)		99.5				114.6				184.2		203.6
Balance Sheet Information
Total Property, Plant and Equipment		2,125.8								2,125.8				1,910.2
Accumulated Depreciation and Amortization		222.8								222.8				166.1
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		1,903.0								1,903.0				1,744.1
Total Assets		4,387.6								4,387.6				3,585.9
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		617.4				464.8				1,641.6		1,223.4
Generation And Marketing [Member] | Other Revenues [Member]
Reportable Segment Information
Revenues		150.7	[2],[14]			(4.5)	[3],[15]			175.3	[4],[16]	13.2	[5],[17]
All Other [Member]
Reportable Segment Information
Revenue from Related Parties	[18]	23.2				28.6				43.5		67.3
Revenues	[18]	26.7				32.6				55.1		72.0
Net Income (Loss)	[18]	(65.1)				(47.3)				(108.3)		(114.6)
Balance Sheet Information
Total Property, Plant and Equipment	[18]	414.5								414.5				407.3
Accumulated Depreciation and Amortization	[18]	189.1								189.1				184.1
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[18]	225.4								225.4				223.2
Total Assets	[18],[19]	6,421.4								6,421.4				5,987.1
Long-term Debt Due Within One Year	[18],[20]	411.2								411.2				410.4
Long-term Debt - Affiliated	[18]	0.0								0.0				0.0
Long-term Debt	[18],[20]	6,027.3								6,027.3				5,873.2
Total Long-term Debt Outstanding	[18],[20]	6,438.5								6,438.5				6,283.6
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[18]	3.5				4.0				11.6		4.7
Revenues		3.1	[2]			(2.2)	[3]			8.4	[4]	(6.7)	[5]
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Related Parties		297.6				241.2				864.6		652.6
Revenues		377.0				304.1				1,104.2		837.8
Net Income (Loss)		145.3				117.5				445.5		308.0
Balance Sheet Information
Total Property, Plant and Equipment		12,359.3								12,359.3				11,345.6
Accumulated Depreciation and Amortization		730.4								730.4				572.8
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		11,628.9								11,628.9				10,772.8
Notes Receivable, Related Parties		0.0								0.0				0.0
Total Assets		11,984.7								11,984.7				11,185.1
Total Long-term Debt Outstanding		4,440.0								4,440.0				3,990.0
Income Tax (Expense) Benefit		36.7				31.7				115.4		82.7
Interest Income		0.1				0.0				0.1		0.9
Interest Expense		36.1				32.7				104.5		95.1
State Transcos [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.2								0.3		0.6
State Transcos [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		79.2				62.9				239.3		184.6
AEPTCo Parent [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0				0.0				0.0		0.0
Revenue from Related Parties		0.0				0.0				0.0		0.0
Revenues		0.0				0.0				0.0		0.0
Net Income (Loss)	[21]	0.1				0.1				0.2		1.1
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		4,343.5								4,343.5				3,948.5
Total Assets	[22]	4,445.3								4,445.3				4,084.0
Total Long-term Debt Outstanding		4,393.4								4,393.4				$ 3,948.5
Income Tax (Expense) Benefit		0.0				0.0				0.0		0.1
Interest Income		40.3				38.4				117.0		111.3
Interest Expense		$ 40.2				$ 38.2				$ 116.6		$ 109.9

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

[11] Elimination of intercompany debt.

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

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

[14] Generation & Marketing includes economic hedge activity.

[15] Generation & Marketing includes economic hedge activity.

[16] Generation & Marketing includes economic hedge activity

[17] Generation & Marketing includes economic hedge activity.

[18] 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.

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

[20] 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.

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

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