Business Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Reportable Segment Information
Vertically Integrated Utilities		$ 2,381.5	$ 2,269.8
Transmission and Distribution Utilities		1,141.2	1,066.4
Generation & Marketing Revenues		477.5	558.8
Sales to AEP Affiliates		0.0	0.0
Corporate and Other Revenues		48.1	38.3
TOTAL REVENUES		4,048.3	3,933.3
Interest Expense		234.0	221.8
Income Tax Expense (Benefit)		102.0	343.2
NET INCOME (LOSS)		456.7	594.2
Balance Sheet Information
Total Property, Plant and Equipment		68,796.3		$ 67,428.5
Accumulated Depreciation and Amortization		17,431.2		17,167.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		51,365.1		50,261.5
Total Assets		65,609.5		64,729.1
Long-term Debt Due Within One Year		2,616.1		1,753.7
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		18,844.9		19,419.6
Total Long-term Debt Outstanding		21,461.0		21,173.3
Vertically Integrated Utilities [Member]
Reportable Segment Information
Vertically Integrated Utilities		2,381.5	2,269.8
Sales to AEP Affiliates		26.5	20.6
TOTAL REVENUES		2,408.0	2,290.4
NET INCOME (LOSS)		232.8	220.5
Balance Sheet Information
Total Property, Plant and Equipment		43,749.8		43,294.4
Accumulated Depreciation and Amortization		13,355.3		13,153.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		30,394.5		30,141.0
Total Assets		37,913.3		37,579.7
Long-term Debt Due Within One Year		1,893.7		1,038.1
Long-term Debt - Affiliated		50.0		50.0
Long-term Debt		9,969.2		10,801.4
Total Long-term Debt Outstanding		11,912.9		11,889.5
Transmission And Distribution Companies [Member]
Reportable Segment Information
Transmission and Distribution Utilities		1,141.2	1,066.4
Sales to AEP Affiliates		21.2	20.0
TOTAL REVENUES		1,162.4	1,086.4
NET INCOME (LOSS)		125.4	119.1
Balance Sheet Information
Total Property, Plant and Equipment		16,790.4		16,371.2
Accumulated Depreciation and Amortization		3,809.8		3,768.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		12,980.6		12,602.9
Total Assets		16,272.6		16,060.7
Long-term Debt Due Within One Year		670.6		663.1
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		4,972.4		4,705.4
Total Long-term Debt Outstanding		5,643.0		5,368.5
AEP Transmission Holdco [Member]
Reportable Segment Information
Transmission Revenue		41.1	27.7
Sales to AEP Affiliates		164.4	128.4
TOTAL REVENUES		205.5	156.1
NET INCOME (LOSS)		104.8	72.8
Balance Sheet Information
Total Property, Plant and Equipment		7,446.6		7,110.2
Accumulated Depreciation and Amortization		200.1		176.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		7,246.5		6,933.6
Total Assets		8,340.5		8,141.8
Long-term Debt Due Within One Year		50.0		50.0
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		2,635.0		2,631.3
Total Long-term Debt Outstanding		2,685.0		2,681.3
Generation And Marketing [Member]
Reportable Segment Information
Generation & Marketing Revenues		477.5	558.8
Sales to AEP Affiliates		27.6	32.6
TOTAL REVENUES		505.1	591.4
NET INCOME (LOSS)		18.1	186.2
Balance Sheet Information
Total Property, Plant and Equipment		786.9		644.6
Accumulated Depreciation and Amortization		70.1		75.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		716.8		569.6
Total Assets		2,123.7		2,009.8
Long-term Debt Due Within One Year		0.1		0.0
Long-term Debt - Affiliated		32.2		32.2
Long-term Debt		(0.3)		(0.3)
Total Long-term Debt Outstanding		32.0		31.9
Other Segments [Member]
Reportable Segment Information
Sales to AEP Affiliates	[1]	17.0	15.9
Corporate and Other Revenues	[1]	7.0	10.6
TOTAL REVENUES	[1]	24.0	26.5
NET INCOME (LOSS)	[1]	(24.4)	(4.4)
Balance Sheet Information
Total Property, Plant and Equipment	[1]	377.7		374.5
Accumulated Depreciation and Amortization	[1]	182.9		180.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[1]	194.8		193.9
Total Assets	[1],[2]	4,552.9		3,959.1
Long-term Debt Due Within One Year	[1]	1.7		2.5
Long-term Debt - Affiliated	[1]	0.0		0.0
Long-term Debt	[1]	1,268.6		1,281.8
Total Long-term Debt Outstanding	[1]	1,270.3		1,284.3
Consolidation, Eliminations [Member]
Reportable Segment Information
Sales to AEP Affiliates		(256.7)	(217.5)
Corporate and Other Revenues		0.0	0.0
TOTAL REVENUES		(256.7)	(217.5)
NET INCOME (LOSS)		0.0	0.0
Balance Sheet Information
Total Property, Plant and Equipment	[3]	(355.1)		(366.4)
Accumulated Depreciation and Amortization	[3]	(187.0)		(186.9)
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[3]	(168.1)		(179.5)
Total Assets	[3],[4]	(3,593.5)		(3,022.0)
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]
Reportable Segment Information
Transmission Revenue		31.3	19.2
Sales to AEP Affiliates		162.1	133.4
Corporate and Other Revenues		0.1	0.1
TOTAL REVENUES		193.5	152.7
Investment Income, Interest and Dividend		0.4	0.2
Interest Expense		19.9	16.0
Income Tax Expense (Benefit)		22.5	28.5
NET INCOME (LOSS)		85.9	57.0
Balance Sheet Information
Total Property, Plant and Equipment		7,108.0		6,780.2
Accumulated Depreciation and Amortization		192.7		170.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		6,915.3		6,609.8
Notes Receivable, Related Parties		0.0		0.0
Total Assets		7,239.9		7,068.1
Long-term Debt Due Within One Year		50.0		50.0
Long-term Debt		2,500.7		2,500.4
Total Long-term Debt Outstanding		2,550.7		2,550.4
AEP Transmission Co [Member] | State Transcos [Member]
Reportable Segment Information
Transmission Revenue		31.3	19.2
Sales to AEP Affiliates		162.1	133.4
Corporate and Other Revenues		0.1	0.1
TOTAL REVENUES		193.5	152.7
Investment Income, Interest and Dividend		0.2	0.1
Interest Expense		19.9	15.8
Income Tax Expense (Benefit)		22.3	28.4
NET INCOME (LOSS)		86.0	56.8
Balance Sheet Information
Total Property, Plant and Equipment		7,108.0		6,780.2
Accumulated Depreciation and Amortization		192.7		170.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		6,915.3		6,609.8
Notes Receivable, Related Parties		0.0		0.0
Total Assets		7,220.0		7,072.9
Total Long-term Debt Outstanding		2,575.0		2,575.0
AEP Transmission Co [Member] | AEPTCo Parent [Member]
Reportable Segment Information
Transmission Revenue		0.0	0.0
Sales to AEP Affiliates		0.0	0.0
Corporate and Other Revenues		0.0	0.0
TOTAL REVENUES		0.0	0.0
Investment Income, Interest and Dividend		25.0	19.1
Interest Expense		24.8	19.2
Income Tax Expense (Benefit)		0.2	0.1
NET INCOME (LOSS)	[5]	(0.1)	0.2
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		2,550.7		2,550.4
Total Assets	[6]	2,637.3		2,590.1
Total Long-term Debt Outstanding		2,550.7		2,550.4
AEP Transmission Co [Member] | Consolidation, Eliminations [Member]
Reportable Segment Information
Transmission Revenue		0.0	0.0
Sales to AEP Affiliates		0.0	0.0
Corporate and Other Revenues		0.0	0.0
TOTAL REVENUES		0.0	0.0
Investment Income, Interest and Dividend	[7]	(24.8)	(19.0)
Interest Expense	[7]	(24.8)	(19.0)
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	[8]	(2,550.7)		(2,550.4)
Total Assets	[9]	(2,617.4)		(2,594.9)
Total Long-term Debt Outstanding	[8]	$ (2,575.0)		$ (2,575.0)

[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] Includes eliminations due to an intercompany capital lease.

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

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

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

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

[8] Elimination of intercompany debt.

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