Business Segments (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017
Reportable Segment Information
Revenue from Contracts with Customers		$ 4,333.1		$ 4,104.7		$ 12,394.6		$ 11,614.5
Sales to AEP Affiliates		0.0		0.0		0.0		0.0
Total Revenues		4,333.1		4,104.7		12,394.6		11,614.5
Interest Expense		256.8		223.3		733.1		668.0
Income Tax Expense		(80.7)		264.0		93.5		797.8
Net Income (Loss)		579.7		556.7		1,566.5		1,527.1
Balance Sheet Information
Total Property, Plant and Equipment		71,197.3				71,197.3				$ 67,428.5
Accumulated Depreciation and Amortization		17,841.6				17,841.6				17,167.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		53,355.7				53,355.7				50,261.5
Total Assets		67,617.4				67,617.4				64,729.1
Long-term Debt Due Within One Year		1,904.2				1,904.2				1,753.7
Long-term Debt - Affiliated		0.0				0.0				0.0
Long-term Debt		20,869.8				20,869.8				19,419.6
Total Long-term Debt Outstanding		22,774.0				22,774.0				21,173.3
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,610.2		2,453.8		7,332.4		6,819.3
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,180.9		1,149.7		3,450.0		3,242.7
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		486.5		441.5		1,399.3		1,386.8
Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		55.5		59.7		212.9		165.7
Total Revenues		58.6	[1]			78.5	[2]
AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[3]	206.8
Sales to AEP Affiliates		148.4		130.1	[4]	453.8	[4]	439.1	[4]
Total Revenues		194.4	[3]	165.6	[4]	586.2	[3],[4]	534.8	[4]
Interest Income		0.5		0.2	[4]	1.3	[4]	0.5	[4]
Interest Expense		19.8		17.1	[4]	60.7	[4]	50.4	[4]
Income Tax Expense		17.6		29.5	[4]	63.7	[4]	108.2	[4]
Net Income (Loss)		78.1		58.6	[4]	244.2	[4]	212.4	[4]
Balance Sheet Information
Total Property, Plant and Equipment	[4]	7,761.6				7,761.6				6,770.5
Accumulated Depreciation and Amortization	[4]	234.6				234.6				152.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[4]	7,527.0				7,527.0				6,617.9
Notes Receivable, Related Parties		0.0				0.0				0.0
Total Assets	[4]	7,998.4				7,998.4				7,082.1
Long-term Debt Due Within One Year		50.0				50.0				50.0
Long-term Debt		2,822.6				2,822.6				2,500.4
Total Long-term Debt Outstanding		2,872.6				2,872.6				2,550.4
AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		46.0		35.6	[4]	132.3	[4]	95.7	[4]
AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		(0.1)	[4]	0.1	[4]	0.0	[4]
Total Revenues	[3]	0.0	[5]			0.0	[6]
Reconciling Adjustments [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0		0.0		0.0
Sales to AEP Affiliates		(247.6)		(226.1)		(674.1)		(727.9)
Total Revenues		(247.6)		(226.1)		(674.1)		(727.9)
Net Income (Loss)		0.0		0.0		0.0		0.0
Balance Sheet Information
Total Property, Plant and Equipment	[7]	(354.4)				(354.4)				(366.4)
Accumulated Depreciation and Amortization	[7]	(186.4)				(186.4)				(186.9)
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[7]	(168.0)				(168.0)				(179.5)
Total Assets	[7],[8]	(3,398.0)				(3,398.0)				(3,022.0)
Long-term Debt Due Within One Year		0.0				0.0				0.0
Long-term Debt - Affiliated		(82.2)				(82.2)				(82.2)
Long-term Debt		0.0				0.0				0.0
Total Long-term Debt Outstanding		(82.2)				(82.2)				(82.2)
Reconciling Adjustments [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		43.0	[1]			0.0	[2]
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	[9]	(25.7)		(19.3)		(75.3)		(57.6)
Interest Expense	[9]	(25.7)		(19.3)		(75.3)		(57.6)
Income Tax Expense		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	[10]	(2,900.0)				(2,900.0)				(2,550.4)
Total Assets	[11]	(2,973.6)				(2,973.6)				(2,594.9)
Total Long-term Debt Outstanding	[10]	(2,900.0)				(2,900.0)				(2,575.0)
Reconciling Adjustments [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0		0.0		0.0
Vertically Integrated Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		26.5		28.4		61.3		73.8
Total Revenues		2,636.7		2,482.2		7,393.7		6,893.1
Net Income (Loss)		345.6		297.3		856.3		639.2
Balance Sheet Information
Total Property, Plant and Equipment		44,553.4				44,553.4				43,294.4
Accumulated Depreciation and Amortization		13,703.3				13,703.3				13,153.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		30,850.1				30,850.1				30,141.0
Total Assets		38,813.2				38,813.2				37,579.7
Long-term Debt Due Within One Year		1,306.1				1,306.1				1,038.1
Long-term Debt - Affiliated		50.0				50.0				50.0
Long-term Debt		11,563.5				11,563.5				10,801.4
Total Long-term Debt Outstanding		12,919.6				12,919.6				11,889.5
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,610.2		2,453.8		7,332.4		6,819.3
Vertically Integrated Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		9.8	[1]			1.1	[2]
Transmission And Distribution Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		30.6		23.6		60.9		70.5
Total Revenues		1,211.5		1,173.3		3,510.9		3,313.2
Net Income (Loss)		145.2		144.0		384.6		374.3
Balance Sheet Information
Total Property, Plant and Equipment		17,619.1				17,619.1				16,371.2
Accumulated Depreciation and Amortization		3,856.7				3,856.7				3,768.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		13,762.4				13,762.4				12,602.9
Total Assets		16,399.1				16,399.1				16,060.7
Long-term Debt Due Within One Year		548.5				548.5				663.1
Long-term Debt - Affiliated		0.0				0.0				0.0
Long-term Debt		5,082.2				5,082.2				4,705.4
Total Long-term Debt Outstanding		5,630.7				5,630.7				5,368.5
Transmission And Distribution Utilities [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,180.9		1,149.7		3,450.0		3,242.7
Transmission And Distribution Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		8.9	[1]			51.9	[2]
AEP Transmission Holdco [Member]
Reportable Segment Information
Sales to AEP Affiliates		135.3		133.4		408.7		456.1
Total Revenues		187.2		178.5		605.2		581.9
Net Income (Loss)		74.2		76.5		280.9		278.3
Balance Sheet Information
Total Property, Plant and Equipment		8,130.3				8,130.3				7,110.2
Accumulated Depreciation and Amortization		244.3				244.3				176.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		7,886.0				7,886.0				6,933.6
Total Assets		9,127.7				9,127.7				8,141.8
Long-term Debt Due Within One Year		50.0				50.0				50.0
Long-term Debt - Affiliated		0.0				0.0				0.0
Long-term Debt		2,966.2				2,966.2				2,631.3
Total Long-term Debt Outstanding		3,016.2				3,016.2				2,681.3
AEP Transmission Holdco [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		51.9		45.1		196.5		125.8
Generation And Marketing [Member]
Reportable Segment Information
Sales to AEP Affiliates		35.1		24.0		88.1		80.7
Total Revenues		521.6		465.5		1,487.4		1,467.5
Net Income (Loss)		5.1		33.7		61.8		246.3
Balance Sheet Information
Total Property, Plant and Equipment		864.1				864.1				644.6
Accumulated Depreciation and Amortization		40.1				40.1				75.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		824.0				824.0				569.6
Total Assets		2,369.3				2,369.3				2,009.8
Long-term Debt Due Within One Year		0.1				0.1				0.0
Long-term Debt - Affiliated		32.2				32.2				32.2
Long-term Debt		(0.3)				(0.3)				(0.3)
Total Long-term Debt Outstanding		32.0				32.0				31.9
Generation And Marketing [Member] | Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		486.5		441.5		1,399.3		1,386.8
Generation And Marketing [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		(5.3)	[1]			18.8	[2]
All Other [Member]
Reportable Segment Information
Sales to AEP Affiliates	[12]	20.1		16.7		55.1		46.8
Total Revenues	[12]	23.7		31.3		71.5		86.7
Net Income (Loss)	[12]	9.6		5.2		(17.1)		(11.0)
Balance Sheet Information
Total Property, Plant and Equipment	[12]	384.8				384.8				374.5
Accumulated Depreciation and Amortization	[12]	183.6				183.6				180.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[12]	201.2				201.2				193.9
Total Assets	[12],[13]	4,306.1				4,306.1				3,959.1
Long-term Debt Due Within One Year	[12]	(0.5)				(0.5)				2.5
Long-term Debt - Affiliated	[12]	0.0				0.0				0.0
Long-term Debt	[12]	1,258.2				1,258.2				1,281.8
Total Long-term Debt Outstanding	[12]	1,257.7				1,257.7				1,284.3
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[12]	3.6		14.6		16.4		39.9
Total Revenues		2.2	[1]			6.7	[2]
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		148.4		130.1	[4]	453.8	[4]	439.1	[4]
Total Revenues		194.4		165.6	[4]	586.2	[4]	534.8	[4]
Interest Income		0.2		0.0	[4]	0.4	[4]	0.1	[4]
Interest Expense		19.8		17.1	[4]	60.7	[4]	50.4	[4]
Income Tax Expense		18.4		29.5	[4]	63.7	[4]	108.0	[4]
Net Income (Loss)		77.1		58.5	[4]	243.6	[4]	212.1	[4]
Balance Sheet Information
Total Property, Plant and Equipment	[4]	7,761.6				7,761.6				6,770.5
Accumulated Depreciation and Amortization	[4]	234.6				234.6				152.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[4]	7,527.0				7,527.0				6,617.9
Notes Receivable, Related Parties		0.0				0.0				0.0
Total Assets	[4]	7,983.6				7,983.6				7,086.9
Total Long-term Debt Outstanding		2,900.0				2,900.0				2,575.0
State Transcos [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		46.0		35.6	[4]	132.3	[4]	95.7	[4]
State Transcos [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		(0.1)	[4]	0.1	[4]	0.0	[4]
AEPTCo Parent [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		0.0		0.0		0.0		0.0
Total Revenues		0.0		0.0		0.0		0.0
Interest Income		26.0		19.5		76.2		58.0
Interest Expense		25.7		19.3		75.3		57.6
Income Tax Expense		(0.8)		0.0		0.0		0.2
Net Income (Loss)	[14]	1.0		0.1		0.6		0.3
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		2,900.0				2,900.0				2,550.4
Total Assets	[15]	2,988.4				2,988.4				2,590.1
Total Long-term Debt Outstanding		2,872.6				2,872.6				$ 2,550.4
AEPTCo Parent [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0		0.0		0.0
AEPTCo Parent [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		$ 0.0		$ 0.0		$ 0.0		$ 0.0

[1] Amounts include affiliated and nonaffiliated revenues.

[2] Amounts include affiliated and nonaffiliated revenues.

[3] The amounts presented reflect the revisions made to AEPTCo’s previously issued financial statements. For additional details on revisions made to AEPTCo’s financial statements, see Note 1- Significant Accounting Matters.

[4] The amounts presented reflect the revisions made to AEPTCo’s previously issued financial statements. For additional details on revisions made to AEPTCo’s financial statements, see Note 1- Significant Accounting Matters.

[5] Amounts include affiliated and nonaffiliated revenues.

[6] Amounts include affiliated and nonaffiliated revenues.

[7] Includes eliminations due to an intercompany capital lease.

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

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

[10] Elimination of intercompany debt.

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

[12] 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.

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

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

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