Business Segments (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Reportable Segment Information
Revenue from Contracts with Customers		$ 14,918.5		$ 15,561.4		$ 16,195.7
Sales to AEP Affiliates		0.0		0.0		0.0
Total Revenues		14,918.5		15,561.4		16,195.7
Asset Impairments and Other Related Charges		0.0		156.4		70.6
Utilities Operating Expense, Depreciation and Amortization		2,682.8		2,514.5		2,286.6
Allowance for Equity Funds Used During Construction		148.1		168.4		132.5
Interest Expense		1,165.7		1,072.5		984.4
Income Tax Expense (Benefit)		40.5		(12.9)		115.3
Equity Earnings (Loss) of Unconsolidated Subsidiaries		91.1		72.1		73.1
Net Income (Loss)		2,196.7		1,919.8		1,931.3
Gross Property Additions		6,246.3		6,969.8		6,325.5
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		84,313.0		79,145.7
Accumulated Depreciation and Amortization		20,411.4		19,007.6
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		63,901.6		60,138.1
Total Assets		80,757.2		75,892.3		68,802.8
Investments in Equity Method Investees		1,406.3		1,356.6
Affiliated Long Term Debt Current				0.0
Long-term Debt Due Within One Year		2,086.1		1,598.7
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		28,986.4		25,126.8
Total Long-term Debt Outstanding		31,072.5		26,725.5
AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,232.7		1,042.1		832.0
Sales to AEP Affiliates		896.3		806.7		598.9
Total Revenues		1,145.7		1,021.4		776.1
Utilities Operating Expense, Depreciation and Amortization		249.0		176.0		133.9
Interest Income		2.4		3.0		2.5
Allowance for Equity Funds Used During Construction		74.0		84.3		70.6
Interest Expense		127.8		97.4		83.2
Income Tax Expense (Benefit)		106.7		117.4		84.1
Net Income (Loss)		423.4		439.7		315.9
Gross Property Additions		1,621.9		1,419.5		1,570.8
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		11,345.6		9,893.2
Accumulated Depreciation and Amortization		572.8		402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,772.8		9,490.9
Notes Receivable, Related Parties		0.0		0.0
Total Assets		11,246.0		9,890.8		8,394.1
Long-term Debt Due Within One Year		50.0		0.0
Long-term Debt		3,898.5		3,427.3
Total Long-term Debt Outstanding		3,948.5		3,427.3
Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		8,753.2		9,245.7		9,556.7
Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		4,238.7		4,319.0		4,552.3
Transmission [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		248.8		214.6		177.0
Generation and Marketing Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		1,621.0		1,721.8		1,818.1
Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		305.6		274.9		268.6
Total Revenues		61.5	[1]	61.7	[2]	25.0	[3]
Other Revenues [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.6		0.1		0.2
Total Revenues		0.0	[4]	0.0	[5]	0.0	[6]
Reconciling Adjustments [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0		0.0
Sales to AEP Affiliates		(1,328.0)		(1,314.8)		(942.4)
Total Revenues		(1,328.0)		(1,314.8)		(942.4)
Asset Impairments and Other Related Charges				0.0		0.0
Utilities Operating Expense, Depreciation and Amortization		0.0		24.5	[7]	57.1	[7]
Interest Expense		(42.1)		(66.1)	[7]	(59.7)	[7]
Income Tax Expense (Benefit)		0.0		0.0		0.0
Equity Earnings (Loss) of Unconsolidated Subsidiaries		0.0		0.0		0.0
Net Income (Loss)		0.0		0.0		0.0
Gross Property Additions		(15.3)		(20.4)		(39.2)
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		0.0		(354.5)	[7]
Accumulated Depreciation and Amortization		0.0		(186.4)	[7]
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		0.0		(168.1)	[7]
Total Assets	[8]	(3,961.7)		(3,801.3)	[7]	(2,714.8)	[7]
Investments in Equity Method Investees		0.0		0.0
Affiliated Long Term Debt Current				(20.0)
Long-term Debt Due Within One Year		0.0		0.0
Long-term Debt - Affiliated		(65.0)		(39.0)
Long-term Debt		0.0		0.0
Total Long-term Debt Outstanding		(65.0)		(59.0)
Reconciling Adjustments [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0		0.0
Sales to AEP Affiliates		0.0		0.0		0.0
Total Revenues		0.0		0.0		0.0
Utilities Operating Expense, Depreciation and Amortization		0.0		0.0		0.0
Interest Income	[9]	(148.1)		(122.1)		(103.4)
Allowance for Equity Funds Used During Construction		0.0		0.0		0.0
Interest Expense	[9]	(148.1)		(122.1)		(103.4)
Income Tax Expense (Benefit)		0.0		0.0		0.0
Net Income (Loss)		0.0		0.0		0.0
Gross Property Additions		0.0		0.0		0.0
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		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	[10]	(3,948.5)		(3,427.3)
Total Assets	[11]	(4,023.1)		(3,493.3)		(2,869.8)
Total Long-term Debt Outstanding	[10]	(3,990.0)		(3,465.0)
Reconciling Adjustments [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		(74.9)	[1]	(139.3)	[2]	(98.0)	[3],[12]
Reconciling Adjustments [Member] | Other Revenues [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0		0.0
Vertically Integrated Utilities [Member]
Reportable Segment Information
Sales to AEP Affiliates		126.2		121.4		88.8
Total Revenues		8,879.4		9,367.1		9,645.5
Asset Impairments and Other Related Charges				92.9		3.4
Utilities Operating Expense, Depreciation and Amortization		1,600.5		1,447.0		1,316.2
Interest Expense		565.0		568.3		567.8
Income Tax Expense (Benefit)		(7.0)		(97.7)		5.7
Equity Earnings (Loss) of Unconsolidated Subsidiaries		2.9		3.0		2.7
Net Income (Loss)		1,064.5		985.6		995.5
Gross Property Additions		2,291.2		2,437.4		2,282.2
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		49,023.3		47,323.7
Accumulated Depreciation and Amortization		15,586.2		14,580.4
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		33,437.1		32,743.3
Total Assets		42,752.7		41,228.8		38,874.3
Investments in Equity Method Investees		37.1		41.7
Affiliated Long Term Debt Current				20.0
Long-term Debt Due Within One Year		1,034.6		704.7
Long-term Debt - Affiliated		65.0		39.0
Long-term Debt		12,375.6		12,162.0
Total Long-term Debt Outstanding		13,475.2		12,925.7
Vertically Integrated Utilities [Member] | Vertically Integrated Utilities [Member]
Reportable Segment Information
Revenue from Contracts with Customers		8,753.2		9,245.7		9,556.7
Vertically Integrated Utilities [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		0.0	[1]	0.0	[2]	(10.5)	[3]
Transmission and Distribution Companies [Member]
Reportable Segment Information
Sales to AEP Affiliates		107.2		163.5		100.8
Total Revenues		4,345.9		4,482.5		4,653.1
Asset Impairments and Other Related Charges				32.5		0.0
Utilities Operating Expense, Depreciation and Amortization		751.1		789.5		734.1
Interest Expense		289.2		243.3		248.1
Income Tax Expense (Benefit)		29.7		(25.2)		42.4
Equity Earnings (Loss) of Unconsolidated Subsidiaries		0.0		0.0		0.0
Net Income (Loss)		496.4		451.0		527.4
Gross Property Additions		2,108.1		2,074.3		2,162.4
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		21,145.0		19,773.3
Accumulated Depreciation and Amortization		3,879.3		3,911.2
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		17,265.7		15,862.1
Total Assets		19,765.9		18,757.5		17,083.4
Investments in Equity Method Investees		2.1		2.5
Affiliated Long Term Debt Current				0.0
Long-term Debt Due Within One Year		588.8		392.2
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		6,661.9		6,248.1
Total Long-term Debt Outstanding		7,250.7		6,640.3
Transmission and Distribution Companies [Member] | Transmission and Distribution Utilities Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers		4,238.7		4,319.0		4,552.3
Transmission and Distribution Companies [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		83.0	[1]	150.0	[2]	102.3	[3]
AEP Transmission Holdco
Reportable Segment Information
Sales to AEP Affiliates		901.4		813.0		555.5
Total Revenues		1,198.8		1,073.2		804.1
Asset Impairments and Other Related Charges				0.0		0.0
Utilities Operating Expense, Depreciation and Amortization		257.6		183.4		137.8
Interest Expense		133.2		103.3		90.7
Income Tax Expense (Benefit)		130.8		136.2		95.3
Equity Earnings (Loss) of Unconsolidated Subsidiaries		82.4		72.8		68.7
Net Income (Loss)		508.5		520.1		373.0
Gross Property Additions		1,649.3		1,458.9		1,614.1
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		11,827.2		10,334.0
Accumulated Depreciation and Amortization		595.7		418.9
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		11,231.5		9,915.1
Total Assets		12,627.3		11,143.5		9,543.7
Investments in Equity Method Investees		831.3		787.5
Affiliated Long Term Debt Current				0.0
Long-term Debt Due Within One Year		52.3		0.0
Long-term Debt - Affiliated		0.0		0.0
Long-term Debt		4,075.7		3,593.8
Total Long-term Debt Outstanding		4,128.0		3,593.8
AEP Transmission Holdco | Transmission [Member]
Reportable Segment Information
Revenue from Contracts with Customers		297.4		260.2		248.6
Generation and Marketing [Member]
Reportable Segment Information
Sales to AEP Affiliates		104.6		135.8		122.2
Total Revenues		1,725.6		1,857.6		1,940.3
Asset Impairments and Other Related Charges				31.0		47.7
Utilities Operating Expense, Depreciation and Amortization		72.8		69.5		41.0
Interest Expense		24.0		30.0		14.9
Income Tax Expense (Benefit)		(108.0)		(53.8)		(49.2)
Equity Earnings (Loss) of Unconsolidated Subsidiaries		3.2		(3.8)		0.5
Net Income (Loss)		216.9		104.1		134.7
Gross Property Additions		197.0		1,005.1		289.7
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		1,910.2		1,650.8
Accumulated Depreciation and Amortization		166.1		99.0
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		1,744.1		1,551.8
Total Assets		3,585.9		3,123.8		1,979.7
Investments in Equity Method Investees		467.0		459.5
Affiliated Long Term Debt Current				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		1,621.0		1,721.8		1,818.1
Generation and Marketing [Member] | Other Revenues [Member]
Reportable Segment Information
Total Revenues		43.6	[1]	59.9	[2]	22.3	[3]
All Other [Member]
Reportable Segment Information
Sales to AEP Affiliates	[13]	88.6		81.1		75.1
Total Revenues	[13]	96.8		95.8		95.1
Asset Impairments and Other Related Charges	[13]			0.0		19.5
Utilities Operating Expense, Depreciation and Amortization	[13]	0.8		0.6		0.4
Interest Expense	[13]	196.4		193.7		122.6
Income Tax Expense (Benefit)	[13]	(5.0)		27.6		21.1
Equity Earnings (Loss) of Unconsolidated Subsidiaries	[13]	2.6		0.1		1.2
Net Income (Loss)	[13]	(89.6)		(141.0)		(99.3)
Gross Property Additions	[13]	16.0		14.5		16.3
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)	[13]	407.3		418.4
Accumulated Depreciation and Amortization	[13]	184.1		184.5
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET	[13]	223.2		233.9
Total Assets	[13],[14]	5,987.1		5,440.0		4,036.5
Investments in Equity Method Investees	[13]	68.8		65.4
Affiliated Long Term Debt Current	[13]			0.0
Long-term Debt Due Within One Year	[13],[15]	410.4		501.8
Long-term Debt - Affiliated	[13]	0.0		0.0
Long-term Debt	[13]	5,873.2	[15]	3,122.9
Total Long-term Debt Outstanding	[13]	6,283.6		3,624.7	[15]
All Other [Member] | Other Revenues [Member]
Reportable Segment Information
Revenue from Contracts with Customers	[13]	8.2		14.7		20.0
Total Revenues		9.8	[1]	(8.9)	[2]	8.9	[3]
State Transcos [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		896.3		806.7		598.9
Total Revenues		1,145.7		1,021.4		776.1
Utilities Operating Expense, Depreciation and Amortization		249.0		176.0		133.9
Interest Income		0.9		1.3		1.3
Allowance for Equity Funds Used During Construction		74.0		84.3		70.6
Interest Expense		127.8		97.4		83.2
Income Tax Expense (Benefit)		106.5		117.1		83.9
Net Income (Loss)		422.3		438.6		314.9
Gross Property Additions		1,621.9		1,419.5		1,570.8
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		11,345.6		9,893.2
Accumulated Depreciation and Amortization		572.8		402.3
TOTAL PROPERTY, PLANT AND EQUIPMENT - NET		10,772.8		9,490.9
Notes Receivable, Related Parties		0.0		0.0
Total Assets		11,185.1		9,865.0		8,406.8
Total Long-term Debt Outstanding		3,990.0		3,465.0
State Transcos [Member] | Transmission [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		248.8		214.6		177.0
State Transcos [Member] | Other Revenues [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.6		0.1		0.2
AEPTCo Parent [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Sales to AEP Affiliates		0.0		0.0		0.0
Total Revenues		0.0		0.0		0.0
Utilities Operating Expense, Depreciation and Amortization		0.0		0.0		0.0
Interest Income		149.6		123.8		104.6
Allowance for Equity Funds Used During Construction		0.0		0.0		0.0
Interest Expense		148.1		122.1		103.4
Income Tax Expense (Benefit)		0.2		0.3		0.2
Net Income (Loss)	[16]	1.1		1.1		1.0
Gross Property Additions		0.0		0.0		0.0
Balance Sheet Information
Property, Plant and Equipment, Gross, Period Increase (Decrease)		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		3,948.5		3,427.3
Total Assets	[17]	4,084.0		3,519.1		2,857.1
Total Long-term Debt Outstanding		3,948.5		3,427.3
AEPTCo Parent [Member] | Transmission [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		0.0		0.0		0.0
AEPTCo Parent [Member] | Other Revenues [Member] | AEP Transmission Co [Member]
Reportable Segment Information
Revenue from Contracts with Customers		$ 0.0		$ 0.0		$ 0.0

[1] Amounts include affiliated and nonaffiliated revenues.

[2] Amounts include affiliated and nonaffiliated revenues.

[3] Amounts include affiliated and nonaffiliated revenues.

[4] Amounts include affiliated and nonaffiliated revenues.

[5] Amounts include affiliated and nonaffiliated revenues.

[6] Amounts include affiliated and nonaffiliated revenues.

[7] Includes eliminations due to an intercompany finance 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 elimination of Notes Receivable from the State Transcos.

[12] 2018 amounts have been revised to reflect the reclassification of $98 million of affiliated revenues between Generation Revenues and Other Revenues. This reclassification did not impact previously reported Total Revenues. Management concluded that these prior period disclosure only errors were immaterial individually and in the aggregate.

[13] 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.

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

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

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

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