Business Segments (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended
		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Reportable Segment Information
Revenue from Contracts with Customers		$ 4,315.0			$ 4,333.1			$ 11,945.4	$ 12,394.6
Sales to AEP Affiliates		0.0			0.0			0.0	0.0
Total Revenues		4,315.0			4,333.1			11,945.4	12,394.6
Interest Expense		275.1			256.8			781.6	733.1
Income Tax Expense (Benefit)		40.6			(80.7)			30.7	93.5
Net Income (Loss)		733.9	$ 459.1	$ 574.1	579.7	$ 530.1	$ 456.7	1,767.1	1,566.5
Balance Sheet Information
Total Property, Plant and Equipment		77,452.9						77,452.9		$ 73,085.2
Accumulated Depreciation and Amortization		18,760.2						18,760.2		17,986.1
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		58,692.7						58,692.7		55,099.1
Total Assets		73,900.7						73,900.7		68,802.8
Long-term Debt Due Within One Year		1,327.7						1,327.7		1,698.5
Long-term Debt - Affiliated		0.0						0.0		0.0
Long-term Debt		24,553.5						24,553.5		21,648.2
Total Long-term Debt Outstanding		25,881.2						25,881.2		23,346.7
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,598.9			2,610.2			7,087.6	7,332.4
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,147.3			1,180.9			3,328.7	3,450.0
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		501.2			486.5			1,323.8	1,399.3
Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		67.6			55.5			205.3	212.9
AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		205.7			148.4			608.0	453.8
Total Revenues		259.7			194.4			770.1	586.2
Interest Income		0.8			0.5			2.1	1.3
Interest Expense		26.4			19.8			69.5	60.7
Income Tax Expense (Benefit)		30.1			17.6			90.7	63.7
Net Income (Loss)		107.6	$ 136.0	$ 104.3	78.1	$ 82.0	$ 84.1	347.9	244.2
Balance Sheet Information
Total Property, Plant and Equipment		9,267.4						9,267.4		8,268.1
Accumulated Depreciation and Amortization		368.8						368.8		271.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		8,898.6						8,898.6		7,996.2
Notes Receivable, Related Parties		0.0						0.0		0.0
Total Assets		9,352.7						9,352.7		8,394.1
Long-term Debt Due Within One Year		85.0						85.0		85.0
Long-term Debt		3,426.9						3,426.9		2,738.0
Total Long-term Debt Outstanding		3,511.9						3,511.9		2,823.0
AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		54.0			46.0			162.1	132.3
AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0			0.0			0.0	0.1
Reconciling Adjustments [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0			0.0			0.0	0.0
Sales to AEP Affiliates		(348.2)			(247.6)			(991.7)	(674.1)
Total Revenues		(348.2)			(247.6)			(991.7)	(674.1)
Net Income (Loss)		0.0			0.0			0.0	0.0
Balance Sheet Information
Total Property, Plant and Equipment	[1]	(354.5)						(354.5)		(354.6)
Accumulated Depreciation and Amortization	[1]	(186.4)						(186.4)		(186.5)
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[1]	(168.1)						(168.1)		(168.1)
Total Assets	[1],[2]	(3,737.9)						(3,737.9)		(2,714.8)
Long-term Debt Due Within One Year		0.0						0.0		0.0
Long-term Debt - Affiliated		(91.2)						(91.2)		(82.2)
Long-term Debt		0.0						0.0		0.0
Total Long-term Debt Outstanding		(91.2)						(91.2)		(82.2)
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	[3]	(31.9)			(25.7)			(88.4)	(75.3)
Interest Expense	[3]	(31.9)			(25.7)			(88.4)	(75.3)
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	[4]	(3,511.9)						(3,511.9)		(2,823.0)
Total Assets	[5]	(3,599.8)						(3,599.8)		(2,869.8)
Total Long-term Debt Outstanding	[4]	(3,550.0)						(3,550.0)		(2,850.0)
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		46.6			26.5			85.0	61.3
Total Revenues		2,645.5			2,636.7			7,172.6	7,393.7
Net Income (Loss)		438.4			345.6			920.8	856.3
Balance Sheet Information
Total Property, Plant and Equipment		46,739.8						46,739.8		45,365.1
Accumulated Depreciation and Amortization		14,359.3						14,359.3		13,822.5
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		32,380.5						32,380.5		31,542.6
Total Assets		40,746.1						40,746.1		38,874.3
Long-term Debt Due Within One Year		687.4						687.4		1,066.3
Long-term Debt - Affiliated		59.0						59.0		50.0
Long-term Debt		12,161.1						12,161.1		11,442.7
Total Long-term Debt Outstanding		12,907.5						12,907.5		12,559.0
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		2,598.9			2,610.2			7,087.6	7,332.4
Transmission And Distribution Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		39.3			30.6			125.6	60.9
Total Revenues		1,186.6			1,211.5			3,454.3	3,510.9
Net Income (Loss)		133.7			145.2			421.6	384.6
Balance Sheet Information
Total Property, Plant and Equipment		19,283.9						19,283.9		18,126.7
Accumulated Depreciation and Amortization		3,907.3						3,907.3		3,833.7
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		15,376.6						15,376.6		14,293.0
Total Assets		17,967.6						17,967.6		17,083.4
Long-term Debt Due Within One Year		391.5						391.5		549.1
Long-term Debt - Affiliated		0.0						0.0		0.0
Long-term Debt		5,868.9						5,868.9		5,048.8
Total Long-term Debt Outstanding		6,260.4						6,260.4		5,597.9
Transmission And Distribution Utilities [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,147.3			1,180.9			3,328.7	3,450.0
AEP Transmission Holdco [Member]
Reportable Segment Information
Sales to AEP Affiliates		207.5			135.3			611.8	408.7
Total Revenues		273.0			187.2			808.3	605.2
Net Income (Loss)		127.0			74.2			407.6	280.9
Balance Sheet Information
Total Property, Plant and Equipment		9,700.4						9,700.4		8,659.5
Accumulated Depreciation and Amortization		383.8						383.8		282.8
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		9,316.6						9,316.6		8,376.7
Total Assets		10,606.7						10,606.7		9,543.7
Long-term Debt Due Within One Year		249.0						249.0		85.0
Long-term Debt - Affiliated		0.0						0.0		0.0
Long-term Debt		3,426.9						3,426.9		2,888.6
Total Long-term Debt Outstanding		3,675.9						3,675.9		2,973.6
AEP Transmission Holdco [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		65.5			51.9			196.5	196.5
Generation And Marketing [Member]
Reportable Segment Information
Sales to AEP Affiliates		32.5			35.1			104.4	88.1
Total Revenues		533.7			521.6			1,428.2	1,487.4
Net Income (Loss)		88.7			5.1			133.1	61.8
Balance Sheet Information
Total Property, Plant and Equipment		1,661.6						1,661.6		893.3
Accumulated Depreciation and Amortization		99.8						99.8		47.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		1,561.8						1,561.8		846.3
Total Assets		3,315.9						3,315.9		1,979.7
Long-term Debt Due Within One Year		0.0						0.0		0.1
Long-term Debt - Affiliated		32.2						32.2		32.2
Long-term Debt		(0.3)						(0.3)		(0.3)
Total Long-term Debt Outstanding		31.9						31.9		32.0
Generation And Marketing [Member] | Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		501.2			486.5			1,323.8	1,399.3
All Other [Member]
Reportable Segment Information
Sales to AEP Affiliates	[6]	22.3			20.1			64.9	55.1
Total Revenues	[6]	24.4			23.7			73.7	71.5
Net Income (Loss)	[6]	(53.9)			9.6			(116.0)	(17.1)
Balance Sheet Information
Total Property, Plant and Equipment	[6]	421.7						421.7		395.2
Accumulated Depreciation and Amortization	[6]	196.4						196.4		186.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[6]	225.3						225.3		208.6
Total Assets	[6],[7]	5,002.3						5,002.3		4,036.5
Long-term Debt Due Within One Year	[6],[8]	(0.2)						(0.2)		(2.0)
Long-term Debt - Affiliated	[6]	0.0						0.0		0.0
Long-term Debt	[6]	3,096.9						3,096.9		2,268.4
Total Long-term Debt Outstanding	[6],[8]	3,096.7						3,096.7		2,266.4
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[6]	2.1			3.6			8.8	16.4
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		205.7			148.4			608.0	453.8
Total Revenues		259.7			194.4			770.1	586.2
Interest Income		0.4			0.2			0.8	0.4
Interest Expense		26.4			19.8			69.5	60.7
Income Tax Expense (Benefit)		30.0			18.4			90.5	63.7
Net Income (Loss)		107.3			77.1			347.1	243.6
Balance Sheet Information
Total Property, Plant and Equipment		9,267.4						9,267.4		8,268.1
Accumulated Depreciation and Amortization		368.8						368.8		271.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		8,898.6						8,898.6		7,996.2
Notes Receivable, Related Parties		0.0						0.0		0.0
Total Assets		9,363.5						9,363.5		8,406.8
Total Long-term Debt Outstanding		3,550.0						3,550.0		2,850.0
State Transcos [Member] | AEP Transmission Co [Member] | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		54.0			46.0			162.1	132.3
State Transcos [Member] | AEP Transmission Co [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0			0.0			0.0	0.1
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		32.3			26.0			89.7	76.2
Interest Expense		31.9			25.7			88.4	75.3
Income Tax Expense (Benefit)		0.1			(0.8)			0.2	0.0
Net Income (Loss)	[9]	0.3			1.0			0.8	0.6
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		3,511.9						3,511.9		2,823.0
Total Assets	[10]	3,589.0						3,589.0		2,857.1
Total Long-term Debt Outstanding		3,511.9						3,511.9		$ 2,823.0
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] 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.