Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($)		3 Months Ended		9 Months Ended			12 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020	Dec. 31, 2020
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 34,578,300,000		$ 34,578,300,000			$ 31,072,500,000
Long Term Debt, Fair Value	[1]	38,925,100,000		38,925,100,000			37,457,000,000
Other Temporary Investments
Cost		238,500,000		238,500,000			214,900,000
Gross Unrealized Gains		33,900,000		33,900,000			31,500,000
Gross Unrealized Losses		0		0			0
Other Short-term Investments		272,400,000		272,400,000			246,400,000
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		6,000,000.0	$ 5,100,000	15,100,000		$ 35,900,000
Purchases of Investments		12,900,000	22,500,000	26,000,000.0		39,500,000
Gross Realized Gains on Investment Sales		2,400,000	200,000	3,600,000		2,400,000
Gross Realized Losses on Investment Sales		0	0	0		200,000
Nuclear Trust Fund Investments
Fair Value		3,609,800,000		3,609,800,000			3,306,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		3,609,800,000		3,609,800,000			3,306,700,000
Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities				1,700,000,000			1,400,000,000
Nuclear Trust Fund Investments
Gross Unrealized Gains				1,726,900,000			1,509,800,000
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		433,900,000	316,600,000	1,556,600,000		1,257,100,000
Purchases of Investments		436,600,000	318,600,000	1,586,300,000		1,290,000,000
Gross Realized Gains on Investment Sales		9,600,000	3,400,000	98,300,000		25,400,000
Gross Realized Losses on Investment Sales		7,000,000.0	500,000	12,500,000		25,200,000
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		292,900,000		292,900,000
After 1 year through 5 years		433,400,000		433,400,000
After 5 years through 10 years		251,500,000		251,500,000
After 10 years		280,900,000		280,900,000
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,200,000,000		1,200,000,000			1,100,000,000
Adjusted Cost of Domestic Equity Securities		634,000,000		634,000,000			654,000,000
Unrealized Loss on Securities				4,000,000			9,000,000
Other than Temporary Impairment Losses, Investments				9,000,000.0			9,200,000
Cash [Member]
Other Temporary Investments
Cost	[2]	77,300,000		77,300,000			68,300,000
Gross Unrealized Gains	[2]	0		0			0
Gross Unrealized Losses	[2]	0		0			0
Other Short-term Investments	[2],[3]	77,300,000		77,300,000			68,300,000
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,258,700,000		1,258,700,000			1,226,200,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,258,700,000		1,258,700,000			1,226,200,000
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				74,100,000			109,000,000.0
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				9,000,000.0			9,200,000
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost	[4]	141,800,000		141,800,000			120,700,000
Gross Unrealized Gains	[4]	1,800,000		1,800,000			2,800,000
Gross Unrealized Losses	[4]	0		0			0
Other Short-term Investments	[4]	143,600,000		143,600,000			123,500,000
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	2,287,200,000		2,287,200,000			2,054,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	2,287,200,000		2,287,200,000			2,054,700,000
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains	[6]			1,652,800,000			1,400,800,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				0			0
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		19,400,000		19,400,000			25,900,000
Gross Unrealized Gains		32,100,000		32,100,000			28,700,000
Gross Unrealized Losses		0		0			0
Other Short-term Investments	[5]	51,500,000		51,500,000			54,600,000
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	63,900,000		63,900,000			25,800,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	63,900,000		63,900,000			25,800,000
Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				0			0
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				0			0
US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		1,135,300,000		1,135,300,000			1,025,600,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,135,300,000		1,135,300,000			1,025,600,000
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				66,900,000			98,500,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				6,800,000			7,100,000
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		86,600,000		86,600,000			86,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		86,600,000		86,600,000			86,300,000
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				6,900,000			9,600,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				2,000,000.0			1,700,000
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		36,800,000		36,800,000			114,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		36,800,000		36,800,000			114,300,000
State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				300,000			900,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				200,000			400,000
AEP Texas Inc. [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		5,216,100,000		5,216,100,000			4,820,400,000
Long Term Debt, Fair Value		5,763,900,000		5,763,900,000			5,682,600,000
AEP Transmission Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,393,400,000		4,393,400,000			3,948,500,000
Long Term Debt, Fair Value		5,074,500,000		5,074,500,000			4,984,300,000
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,937,800,000		4,937,800,000			4,834,100,000
Long Term Debt, Fair Value		6,067,000,000		6,067,000,000			6,391,800,000
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,231,100,000		3,231,100,000			3,029,900,000
Long Term Debt, Fair Value		3,790,500,000		3,790,500,000			3,775,300,000
Nuclear Trust Fund Investments
Fair Value		3,609,800,000		3,609,800,000			3,306,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		3,609,800,000		3,609,800,000			3,306,700,000
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities				1,700,000,000			1,400,000,000
Nuclear Trust Fund Investments
Gross Unrealized Gains				1,726,900,000			1,509,800,000
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		433,900,000	316,600,000	1,556,600,000		1,257,100,000
Purchases of Investments		436,600,000	318,600,000	1,586,300,000		1,290,000,000
Gross Realized Gains on Investment Sales		9,600,000	3,400,000	98,300,000		25,400,000
Gross Realized Losses on Investment Sales		7,000,000.0	$ 500,000	12,500,000		$ 25,200,000
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		292,900,000		292,900,000
After 1 year through 5 years		433,400,000		433,400,000
After 5 years through 10 years		251,500,000		251,500,000
After 10 years		280,900,000		280,900,000
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,200,000,000		1,200,000,000			1,100,000,000
Adjusted Cost of Domestic Equity Securities		634,000,000		634,000,000			654,000,000
Unrealized Loss on Securities				4,000,000			9,000,000
Other than Temporary Impairment Losses, Investments				9,000,000.0			9,200,000
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,258,700,000		1,258,700,000			1,226,200,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,258,700,000		1,258,700,000			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				74,100,000			109,000,000.0
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				9,000,000.0			9,200,000
Indiana Michigan Power Co [Member] | Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	2,287,200,000		2,287,200,000			2,054,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	2,287,200,000		2,287,200,000			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				1,652,800,000	[6]		1,400,800,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				0			0
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	63,900,000		63,900,000			25,800,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	63,900,000		63,900,000			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
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				0			0
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		1,135,300,000		1,135,300,000			1,025,600,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,135,300,000		1,135,300,000			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				66,900,000			98,500,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				6,800,000			7,100,000
Indiana Michigan Power Co [Member] | Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		86,600,000		86,600,000			86,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		86,600,000		86,600,000			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				6,900,000			9,600,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				2,000,000.0			1,700,000
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		36,800,000		36,800,000			114,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		36,800,000		36,800,000			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				300,000			900,000
Fair Value Measurements (Textuals)
Other than Temporary Impairment Losses, Investments				200,000			400,000
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,468,100,000		3,468,100,000			2,430,200,000
Long Term Debt, Fair Value		3,948,600,000		3,948,600,000			3,154,900,000
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,913,300,000		1,913,300,000			1,373,800,000
Long Term Debt, Fair Value		2,169,200,000		2,169,200,000			1,732,100,000
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,129,900,000		3,129,900,000			2,636,400,000
Long Term Debt, Fair Value		3,534,000,000		3,534,000,000			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		$ 1,600,000,000			$ 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 September 30, 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 $1.7 billion and $1.4 billion and unrealized losses of $4 million and $9 million as of September 30, 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.