Business Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Reportable Segment Information
Revenue from Contracts with Customers		$ 3,747.5	$ 4,056.8
Sales to AEP Affiliates		0.0	0.0
Total Revenues		3,747.5	4,056.8
Interest Expense		292.1	255.8
Income Tax Expense (Benefit)		46.5	44.5
Net Income (Loss)		499.3	574.1
Balance Sheet Information
Total Property, Plant and Equipment		80,417.0		$ 79,145.7
Accumulated Depreciation and Amortization		19,368.1		19,007.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		61,048.9		60,138.1
Total Assets		77,724.0		75,892.3
Affiliated Long Term Debt Current		0.0		0.0
Long-term Debt Due Within One Year		2,109.7		1,598.7
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		25,783.0		25,126.8
Total Long-term Debt Outstanding		27,892.7		26,725.5
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,193.0	2,372.3
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,075.2	1,179.8
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		408.4	439.7
Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		70.9	65.0
AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		233.7	193.2
Total Revenues		295.6	243.5
Interest Income		0.8	0.7
Interest Expense		29.6	21.7
Income Tax Expense (Benefit)		31.8	27.6
Net Income (Loss)		117.8	104.3
Balance Sheet Information
Total Property, Plant and Equipment		10,221.2		9,893.2
Accumulated Depreciation and Amortization		445.8		402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		9,775.4		9,490.9
Notes Receivable, Related Parties		0.0		0.0
Total Assets		10,199.9		9,890.8
Long-term Debt		3,427.8		3,427.3
Total Long-term Debt Outstanding		3,427.8		3,427.3
AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		61.3	50.3
AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.6	0.0
Reconciling Adjustments [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0	0.0
Sales to AEP Affiliates		(354.8)	(332.2)
Total Revenues		(354.8)	(332.2)
Net Income (Loss)		0.0	0.0
Balance Sheet Information
Total Property, Plant and Equipment	[1]	(354.5)		(354.5)
Accumulated Depreciation and Amortization	[1]	(186.5)		(186.4)
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[1]	(168.0)		(168.1)
Total Assets	[1],[2]	(3,923.8)		(3,801.3)
Affiliated Long Term Debt Current		(20.0)		(20.0)
Long-term Debt Due Within One Year		0.0		0.0
Long-term Debt - Affiliated		(39.0)		(39.0)
Long-term Debt		0.0		0.0
Total Long-term Debt Outstanding		(59.0)		(59.0)
Reconciling Adjustments [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0	0.0
Sales to AEP Affiliates		0.0	0.0
Total Revenues		0.0	0.0
Interest Income	[3]	(33.4)	(27.9)
Interest Expense	[3]	(33.4)	(27.9)
Income Tax Expense (Benefit)		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	[4]	(3,427.8)		(3,427.3)
Total Assets	[5]	(3,513.7)		(3,493.3)
Total Long-term Debt Outstanding	[4]	(3,465.0)		(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		33.7	31.0
Total Revenues		2,226.7	2,403.3
Net Income (Loss)		246.3	303.6
Balance Sheet Information
Total Property, Plant and Equipment		47,764.3		47,323.7
Accumulated Depreciation and Amortization		14,821.8		14,580.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		32,942.5		32,743.3
Total Assets		41,020.5		41,228.8
Affiliated Long Term Debt Current		20.0		20.0
Long-term Debt Due Within One Year		1,316.3		704.7
Long-term Debt - Affiliated		39.0		39.0
Long-term Debt		11,641.0		12,162.0
Total Long-term Debt Outstanding		13,016.3		12,925.7
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,193.0	2,372.3
Transmission And Distribution Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		31.7	42.2
Total Revenues		1,106.9	1,222.0
Net Income (Loss)		116.2	156.5
Balance Sheet Information
Total Property, Plant and Equipment		20,182.8		19,773.3
Accumulated Depreciation and Amortization		3,964.6		3,911.2
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		16,218.2		15,862.1
Total Assets		18,892.5		18,757.5
Affiliated Long Term Debt Current		0.0		0.0
Long-term Debt Due Within One Year		289.0		392.2
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		6,585.5		6,248.1
Total Long-term Debt Outstanding		6,874.5		6,640.3
Transmission And Distribution Utilities [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,075.2	1,179.8
AEP Transmission Holdco [Member]
Reportable Segment Information
Sales to AEP Affiliates		237.1	195.2
Total Revenues		310.2	256.4
Net Income (Loss)		141.6	125.2
Balance Sheet Information
Total Property, Plant and Equipment		10,662.9		10,334.0
Accumulated Depreciation and Amortization		464.0		418.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,198.9		9,915.1
Total Assets		11,484.8		11,143.5
Affiliated Long Term Debt Current		0.0		0.0
Long-term Debt Due Within One Year		0.0		0.0
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		3,600.3		3,593.8
Total Long-term Debt Outstanding		3,600.3		3,593.8
AEP Transmission Holdco [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		73.1	61.2
Generation And Marketing [Member]
Reportable Segment Information
Sales to AEP Affiliates		30.2	42.1
Total Revenues		438.6	481.8
Net Income (Loss)		30.5	39.2
Balance Sheet Information
Total Property, Plant and Equipment		1,753.2		1,650.8
Accumulated Depreciation and Amortization		116.9		99.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		1,636.3		1,551.8
Total Assets		3,216.4		3,123.8
Affiliated Long Term Debt Current		0.0		0.0
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		408.4	439.7
All Other [Member]
Reportable Segment Information
Sales to AEP Affiliates	[6]	22.1	21.7
Total Revenues	[6]	19.9	25.5
Net Income (Loss)	[6]	(35.3)	(50.4)
Balance Sheet Information
Total Property, Plant and Equipment	[6]	408.3		418.4
Accumulated Depreciation and Amortization	[6]	187.3		184.5
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[6]	221.0		233.9
Total Assets	[6],[7]	7,033.6		5,440.0
Affiliated Long Term Debt Current	[6]	0.0		0.0
Long-term Debt Due Within One Year	[6],[8]	504.4		501.8
Long-term Debt - Affiliated	[6]	0.0		0.0
Long-term Debt	[6],[8]	3,956.2		3,122.9
Total Long-term Debt Outstanding	[6]	4,460.6		3,624.7
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[6]	(2.2)	3.8
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		233.7	193.2
Total Revenues		295.6	243.5
Interest Income		0.2	0.2
Interest Expense		29.6	21.7
Income Tax Expense (Benefit)		31.8	27.6
Net Income (Loss)		117.3	104.2
Balance Sheet Information
Total Property, Plant and Equipment		10,221.2		9,893.2
Accumulated Depreciation and Amortization		445.8		402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		9,775.4		9,490.9
Notes Receivable, Related Parties		0.0		0.0
Total Assets		10,150.9		9,865.0
Total Long-term Debt Outstanding		3,465.0		3,465.0
State Transcos [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		61.3	50.3
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
Sales to AEP Affiliates		0.0	0.0
Total Revenues		0.0	0.0
Interest Income		34.0	28.4
Interest Expense		33.4	27.9
Income Tax Expense (Benefit)		0.0	0.0
Net Income (Loss)	[9]	0.5	$ 0.1
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		3,427.8		3,427.3
Total Assets	[10]	3,562.7		3,519.1
Total Long-term Debt Outstanding		3,427.8		$ 3,427.3
AEPTCo Parent [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		$ 0.0

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

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

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

[4] Elimination of intercompany debt.

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

[6] 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.

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

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

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

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