Business Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2018
Revenue from Contracts with Customers		$ 4,056.8		$ 4,048.3
Reportable Segment Information
Sales to AEP Affiliates		0.0		0.0
TOTAL REVENUES		4,056.8		4,048.3
Interest Expense		255.8		234.0
Income Tax Expense (Benefit)		44.5		102.0
NET INCOME (LOSS)		574.1		456.7
Balance Sheet Information
Total Property, Plant and Equipment		74,151.2				$ 73,085.2
Accumulated Depreciation and Amortization		18,182.6				17,986.1
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		55,968.6				55,099.1
Total Assets		70,722.0				68,802.8
Long-term Debt Due Within One Year		1,528.5				1,698.5
Long-term Debt - Affiliated		0.0				0.0
Long-term Debt		22,898.2				21,648.2
Total Long-term Debt Outstanding		24,426.7				23,346.7
Vertically Integrated Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		31.0		26.5
TOTAL REVENUES		2,403.3		2,408.0
NET INCOME (LOSS)		303.6		232.8
Balance Sheet Information
Total Property, Plant and Equipment		45,684.3				45,365.1
Accumulated Depreciation and Amortization		13,944.5				13,822.5
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		31,739.8				31,542.6
Total Assets		40,085.7				38,874.3
Long-term Debt Due Within One Year		912.1				1,066.3
Long-term Debt - Affiliated		50.0				50.0
Long-term Debt		11,999.5				11,442.7
Total Long-term Debt Outstanding		12,961.6				12,559.0
Transmission And Distribution Companies [Member]
Reportable Segment Information
Sales to AEP Affiliates		42.2		21.2
TOTAL REVENUES		1,222.0		1,162.4
NET INCOME (LOSS)		156.5		125.4
Balance Sheet Information
Total Property, Plant and Equipment		18,526.1				18,126.7
Accumulated Depreciation and Amortization		3,856.1				3,833.7
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		14,670.0				14,293.0
Total Assets		17,419.0				17,083.4
Long-term Debt Due Within One Year		533.3				549.1
Long-term Debt - Affiliated		0.0				0.0
Long-term Debt		4,938.6				5,048.8
Total Long-term Debt Outstanding		5,471.9				5,597.9
AEP Transmission Holdco [Member]
Reportable Segment Information
TOTAL REVENUES		256.4		205.5
Balance Sheet Information
Total Property, Plant and Equipment		8,973.2				8,659.5
Accumulated Depreciation and Amortization		318.8				282.8
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		8,654.4				8,376.7
Total Assets		9,790.2				9,543.7
Long-term Debt Due Within One Year		85.0				85.0
Long-term Debt - Affiliated		0.0				0.0
Long-term Debt		2,895.3				2,888.6
Total Long-term Debt Outstanding		2,980.3				2,973.6
Transmission Operations [Member]
Reportable Segment Information
Sales to AEP Affiliates		195.2		164.4
TOTAL REVENUES		256.4		205.5
NET INCOME (LOSS)		125.2		104.8
Generation And Marketing [Member]
Reportable Segment Information
Sales to AEP Affiliates		42.1		27.6
TOTAL REVENUES		481.8		505.1
NET INCOME (LOSS)		39.2		18.1
Balance Sheet Information
Total Property, Plant and Equipment		915.6				893.3
Accumulated Depreciation and Amortization		58.7				47.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		856.9				846.3
Total Assets		1,960.1				1,979.7
Long-term Debt Due Within One Year		0.0				0.1
Long-term Debt - Affiliated		32.2				32.2
Long-term Debt		(0.3)				(0.3)
Total Long-term Debt Outstanding		31.9				32.0
Other Segments [Member]
Reportable Segment Information
Sales to AEP Affiliates	[1]	21.7		17.0
TOTAL REVENUES	[1]	25.5		24.0
NET INCOME (LOSS)	[1]	(50.4)		(24.4)
Balance Sheet Information
Total Property, Plant and Equipment	[1]	406.4				395.2
Accumulated Depreciation and Amortization	[1]	190.9				186.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[1]	215.5				208.6
Total Assets	[1],[2]	4,341.2				4,036.5
Long-term Debt Due Within One Year	[1],[3]	(1.9)				(2.0)
Long-term Debt - Affiliated	[1]	0.0				0.0
Long-term Debt	[1]	3,065.1				2,268.4
Total Long-term Debt Outstanding	[1],[3]	3,063.2				2,266.4
Consolidation, Eliminations [Member]
Revenue from Contracts with Customers		0.0		0.0
Reportable Segment Information
Sales to AEP Affiliates		(332.2)		(256.7)
TOTAL REVENUES		(332.2)		(256.7)
NET INCOME (LOSS)		0.0		0.0
Balance Sheet Information
Total Property, Plant and Equipment	[4]	(354.4)				(354.6)
Accumulated Depreciation and Amortization	[4]	(186.4)				(186.5)
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[4]	(168.0)				(168.1)
Total Assets	[4],[5]	(2,874.2)				(2,714.8)
Long-term Debt Due Within One Year		0.0				0.0
Long-term Debt - Affiliated		(82.2)				(82.2)
Long-term Debt		0.0				0.0
Total Long-term Debt Outstanding		(82.2)				(82.2)
AEP Transmission Co [Member]
Revenue from Contracts with Customers		245.2		187.0	[6]
Reportable Segment Information
Sales to AEP Affiliates		193.2		160.7	[7]
TOTAL REVENUES		243.5		191.7	[6],[7]
Investment Income, Interest and Dividend		0.7		0.4	[7]
Interest Expense		21.7		20.3	[7]
Income Tax Expense (Benefit)		27.6		22.0	[7]
NET INCOME (LOSS)		104.3		84.1	[7]
Balance Sheet Information
Total Property, Plant and Equipment		8,567.2				8,268.1
Accumulated Depreciation and Amortization		306.7				271.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		8,260.5				7,996.2
Notes Receivable, Related Parties		0.0				0.0
Total Assets		8,616.1				8,394.1
Long-term Debt Due Within One Year		85.0				85.0
Long-term Debt		2,738.4				2,738.0
Total Long-term Debt Outstanding		2,823.4				2,823.0
AEP Transmission Co [Member] | State Transcos [Member]
Reportable Segment Information
Sales to AEP Affiliates		193.2		160.7	[7]
TOTAL REVENUES		243.5		191.7	[7]
Investment Income, Interest and Dividend		0.2		0.2	[7]
Interest Expense		21.7		20.3	[7]
Income Tax Expense (Benefit)		27.6		21.7	[7]
NET INCOME (LOSS)		104.2		84.1	[7]
Balance Sheet Information
Total Property, Plant and Equipment		8,567.2				8,268.1
Accumulated Depreciation and Amortization		306.7				271.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		8,260.5				7,996.2
Notes Receivable, Related Parties		0.0				0.0
Total Assets		8,584.0				8,406.8
Total Long-term Debt Outstanding		2,850.0				2,850.0
AEP Transmission Co [Member] | AEPTCo Parent [Member]
Reportable Segment Information
Sales to AEP Affiliates		0.0		0.0
TOTAL REVENUES		0.0		0.0
Investment Income, Interest and Dividend		28.4		25.0
Interest Expense		27.9		24.8
Income Tax Expense (Benefit)		0.0		0.3
NET INCOME (LOSS)	[8]	0.1		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		2,823.4				2,823.0
Total Assets	[9]	2,928.1				2,857.1
Total Long-term Debt Outstanding		2,823.4				2,823.0
AEP Transmission Co [Member] | Consolidation, Eliminations [Member]
Revenue from Contracts with Customers		0.0		0.0
Reportable Segment Information
Sales to AEP Affiliates		0.0		0.0
TOTAL REVENUES		0.0		0.0
Investment Income, Interest and Dividend	[10]	(27.9)		(24.8)
Interest Expense	[10]	(27.9)		(24.8)
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	[11]	(2,823.4)				(2,823.0)
Total Assets	[12]	(2,896.0)				(2,869.8)
Total Long-term Debt Outstanding	[11]	(2,850.0)				$ (2,850.0)
Transmission and Distribution Utilities Revenues [Member]
Revenue from Contracts with Customers		1,179.8		1,141.2
Transmission and Distribution Utilities Revenues [Member] | Transmission And Distribution Companies [Member]
Revenue from Contracts with Customers		1,179.8		1,141.2
Electric Transmission [Member] | Transmission Operations [Member]
Revenue from Contracts with Customers		61.2		41.1
Electric Transmission [Member] | AEP Transmission Co [Member]
Revenue from Contracts with Customers		50.3		30.9	[7]
Electric Transmission [Member] | AEP Transmission Co [Member] | State Transcos [Member]
Revenue from Contracts with Customers		50.3		30.9	[7]
Electric Transmission [Member] | AEP Transmission Co [Member] | AEPTCo Parent [Member]
Revenue from Contracts with Customers		0.0		0.0
Generation & Marketing Revenues [Member]
Revenue from Contracts with Customers		439.7		477.5
Generation & Marketing Revenues [Member] | Generation And Marketing [Member]
Revenue from Contracts with Customers		439.7		477.5
Other Revenues [Member]
Revenue from Contracts with Customers		65.0		48.1
Reportable Segment Information
TOTAL REVENUES		50.8	[13]	28.5	[14]
Other Revenues [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
TOTAL REVENUES		0.0	[13]	5.5	[14]
Other Revenues [Member] | Transmission And Distribution Companies [Member]
Reportable Segment Information
TOTAL REVENUES		39.4	[13]	21.7	[14]
Other Revenues [Member] | AEP Transmission Holdco [Member]
Reportable Segment Information
TOTAL REVENUES		0.0	[13]	0.0	[14]
Other Revenues [Member] | Generation And Marketing [Member]
Reportable Segment Information
TOTAL REVENUES		9.2	[13]	21.0	[14]
Other Revenues [Member] | Other Segments [Member]
Revenue from Contracts with Customers	[1]	3.8		7.0
Reportable Segment Information
TOTAL REVENUES		2.2	[13]	2.0	[14]
Other Revenues [Member] | Consolidation, Eliminations [Member]
Reportable Segment Information
TOTAL REVENUES		0.0	[13]	(21.7)	[14]
Other Revenues [Member] | AEP Transmission Co [Member]
Revenue from Contracts with Customers		0.0		0.1	[7]
Reportable Segment Information
TOTAL REVENUES		0.0	[15]	0.0	[6],[16]
Other Revenues [Member] | AEP Transmission Co [Member] | State Transcos [Member]
Revenue from Contracts with Customers	[7]			0.1
Other Revenues [Member] | AEP Transmission Co [Member] | AEPTCo Parent [Member]
Revenue from Contracts with Customers				0.0
Electricity [Member]
Revenue from Contracts with Customers		2,372.3		2,381.5
Electricity [Member] | Vertically Integrated Utilities [Member]
Revenue from Contracts with Customers		$ 2,372.3		$ 2,381.5

[1] 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 and interest expense and other nonallocated costs.

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

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

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

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

[6] The amounts presented reflect the revisions made to AEPTCo’s previously issued financial statements. See the “Revisions to Previously Issued Financial Statements” section of Note 1 for additional information.

[7] The amounts presented reflect the revisions made to AEPTCo’s previously issued financial statements. See the “Revisions to Previously Issued Financial Statements” section of Note 1 for additional information.

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

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

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

[11] Elimination of intercompany debt.

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

[13] Amounts include affiliated and nonaffiliated revenues.

[14] Amounts include affiliated and nonaffiliated revenues.

[15] Amounts include affiliated and nonaffiliated revenues.

[16] Amounts include affiliated and nonaffiliated revenues.