Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($)		3 Months Ended			12 Months Ended
		Mar. 31, 2021		Mar. 31, 2020	Dec. 31, 2020
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 32,345,000,000.0			$ 31,072,500,000
Long Term Debt, Fair Value	[1]	35,802,400,000			37,457,000,000.0
Other Temporary Investments
Cost		216,200,000			214,900,000
Gross Unrealized Gains		33,700,000			31,500,000
Gross Unrealized Losses		0			0
Other Short-term Investments		249,900,000			246,400,000
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		5,500,000		$ 23,200,000
Purchases of Investments		700,000		6,700,000
Gross Realized Gains on Investment Sales		100,000		2,000,000.0
Gross Realized Losses on Investment Sales		0		100,000
Nuclear Trust Fund Investments
Fair Value		3,414,300,000			3,306,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		3,414,300,000			3,306,700,000
Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities		1,500,000,000			1,400,000,000
Nuclear Trust Fund Investments
Gross Unrealized Gains		1,603,500,000			1,509,800,000
Other-Than-Temporary Impairments		(16,300,000)			(9,200,000)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		320,000,000.0		612,400,000
Purchases of Investments		336,900,000		626,000,000.0
Gross Realized Gains on Investment Sales		5,400,000		10,900,000
Gross Realized Losses on Investment Sales		4,200,000		17,000,000.0
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		320,500,000
After 1 year through 5 years		334,700,000
After 5 years through 10 years		233,600,000
After 10 years		270,300,000
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,100,000,000			1,100,000,000
Adjusted Cost of Domestic Equity Securities		664,000,000			654,000,000
Unrealized Loss on Securities		5,000,000			9,000,000
Cash [Member]
Other Temporary Investments
Cost	[2]	74,600,000			68,300,000
Gross Unrealized Gains	[2]	0			0
Gross Unrealized Losses	[2]	0			0
Other Short-term Investments	[2],[3]	74,600,000			68,300,000
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,159,100,000			1,226,200,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,159,100,000			1,226,200,000
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		60,000,000.0			109,000,000.0
Other-Than-Temporary Impairments		(16,300,000)			(9,200,000)
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost	[4]	116,700,000			120,700,000
Gross Unrealized Gains	[4]	2,000,000.0			2,800,000
Gross Unrealized Losses	[4]	0			0
Other Short-term Investments	[4]	118,700,000			123,500,000
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	2,207,500,000			2,054,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	2,207,500,000			2,054,700,000
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains	[6]	1,543,500,000			1,400,800,000
Other-Than-Temporary Impairments		0			0
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		24,900,000			25,900,000
Gross Unrealized Gains		31,700,000			28,700,000
Gross Unrealized Losses		0			0
Other Short-term Investments	[5]	56,600,000			54,600,000
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	47,700,000			25,800,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	47,700,000			25,800,000
Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		0			0
Other-Than-Temporary Impairments		0			0
US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		998,900,000			1,025,600,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		998,900,000			1,025,600,000
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		54,800,000			98,500,000
Other-Than-Temporary Impairments		(13,000,000.0)			(7,100,000)
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		76,400,000			86,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		76,400,000			86,300,000
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		4,800,000			9,600,000
Other-Than-Temporary Impairments		(2,600,000)			(1,700,000)
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		83,800,000			114,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		83,800,000			114,300,000
State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		400,000			900,000
Other-Than-Temporary Impairments		(700,000)			(400,000)
AEP Texas Inc. [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,810,200,000			4,820,400,000
Long Term Debt, Fair Value		5,235,600,000			5,682,600,000
AEP Transmission Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,949,000,000.0			3,948,500,000
Long Term Debt, Fair Value		4,460,100,000			4,984,300,000
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,966,200,000			4,834,100,000
Long Term Debt, Fair Value		5,871,100,000			6,391,800,000
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,006,300,000			3,029,900,000
Long Term Debt, Fair Value		3,422,900,000			3,775,300,000
Nuclear Trust Fund Investments
Fair Value		3,414,300,000			3,306,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		3,414,300,000			3,306,700,000
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities		1,500,000,000			1,400,000,000
Nuclear Trust Fund Investments
Gross Unrealized Gains		1,603,500,000			1,509,800,000
Other-Than-Temporary Impairments		(16,300,000)			(9,200,000)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		320,000,000.0		612,400,000
Purchases of Investments		336,900,000		626,000,000.0
Gross Realized Gains on Investment Sales		5,400,000		10,900,000
Gross Realized Losses on Investment Sales		4,200,000		$ 17,000,000.0
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		320,500,000
After 1 year through 5 years		334,700,000
After 5 years through 10 years		233,600,000
After 10 years		270,300,000
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,100,000,000			1,100,000,000
Adjusted Cost of Domestic Equity Securities		664,000,000			654,000,000
Unrealized Loss on Securities		5,000,000			9,000,000
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,159,100,000			1,226,200,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,159,100,000			1,226,200,000
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		60,000,000.0			109,000,000.0
Other-Than-Temporary Impairments		(16,300,000)			(9,200,000)
Indiana Michigan Power Co [Member] | Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	2,207,500,000			2,054,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	2,207,500,000			2,054,700,000
Indiana Michigan Power Co [Member] | Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		1,543,500,000	[6]		1,400,800,000
Other-Than-Temporary Impairments		0			0
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	47,700,000			25,800,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	47,700,000			25,800,000
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		0			0
Other-Than-Temporary Impairments		0			0
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		998,900,000			1,025,600,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		998,900,000			1,025,600,000
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		54,800,000			98,500,000
Other-Than-Temporary Impairments		(13,000,000.0)			(7,100,000)
Indiana Michigan Power Co [Member] | Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		76,400,000			86,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		76,400,000			86,300,000
Indiana Michigan Power Co [Member] | Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		4,800,000			9,600,000
Other-Than-Temporary Impairments		(2,600,000)			(1,700,000)
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		83,800,000			114,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		83,800,000			114,300,000
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		400,000			900,000
Other-Than-Temporary Impairments		(700,000)			(400,000)
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,876,300,000			2,430,200,000
Long Term Debt, Fair Value		3,316,100,000			3,154,900,000
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,623,800,000			1,373,800,000
Long Term Debt, Fair Value		1,842,400,000			1,732,100,000
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,131,400,000			2,636,400,000
Long Term Debt, Fair Value		3,444,800,000			3,210,100,000
Equity Units [Member]
Book Values and Fair Values of Long - term Debt
Long Term Debt, Fair Value		$ 1,600,000,000			$ 1,700,000,000

[1] The fair value amounts include debt related to AEP’s Equity Units and had a fair value of $1.6 billion and $1.7 billion as of March 31, 2021 and December 31, 2020, respectively. See “Equity Units” section of Note 12 for additional information.

[2] Primarily represents amounts held for the repayment of debt.

[3] Amounts in “Other’’ column primarily represent cash deposits in bank accounts with financial institutions or third-parties.  Level 1 and Level 2 amounts primarily represent investments in money market funds.

[4] Primarily short and intermediate maturities which may be sold and do not contain maturity dates.

[5] Amounts represent publicly traded equity securities and equity-based mutual funds.

[6] Amount reported as Gross Unrealized Gains includes unrealized gains of $1.5 billion and $1.4 billion and unrealized losses of $5 million and $9 million as of March 31, 2021 and December 31, 2020, respectively.

[7] Amounts in “Other’’ column primarily represent accrued interest receivables from financial institutions.  Level 1 amounts primarily represent investments in money market funds.