Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($)		3 Months Ended		9 Months Ended			12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 30,067,100,000		$ 30,067,100,000			$ 26,725,500,000
Long Term Debt, Fair Value	[1]	35,603,200,000		35,603,200,000			30,172,000,000.0
Other Temporary Investments
Cost		237,700,000		237,700,000			367,100,000
Gross Unrealized Gains		25,400,000		25,400,000			21,400,000
Gross Unrealized Losses		0		0			0
Other Short-term Investments		263,100,000		263,100,000			388,500,000
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		5,100,000	$ 2,800,000	35,900,000		$ 2,800,000
Purchases of Investments		22,500,000	26,900,000	39,500,000		35,800,000
Gross Realized Gains on Investment Sales		200,000	0	2,400,000		0
Gross Realized Losses on Investment Sales		0	0	200,000		0
Nuclear Trust Fund Investments
Fair Value		3,075,900,000		3,075,900,000			2,975,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		3,075,900,000		3,075,900,000			2,975,700,000
Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities				1,200,000,000			1,100,000,000
Nuclear Trust Fund Investments
Gross Unrealized Gains				1,288,500,000			1,205,900,000
Other-Than-Temporary Impairments				(7,600,000)			(7,900,000)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		316,600,000	671,900,000	1,257,100,000		871,400,000
Purchases of Investments		318,600,000	689,100,000	1,290,000,000.0		915,700,000
Gross Realized Gains on Investment Sales		3,400,000	10,900,000	25,400,000		26,600,000
Gross Realized Losses on Investment Sales		500,000	7,100,000	25,200,000		15,100,000
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		291,600,000		291,600,000
After 1 year through 5 years		355,900,000		355,900,000
After 5 years through 10 years		255,100,000		255,100,000
After 10 years		346,100,000		346,100,000
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,100,000,000		1,100,000,000			1,100,000,000
Adjusted Cost of Domestic Equity Securities		628,000,000		628,000,000			623,000,000
Unrealized Loss on Securities				17,000,000			5,000,000
Cash [Member]
Other Temporary Investments
Cost	[2]	79,600,000		79,600,000			214,700,000
Gross Unrealized Gains	[2]	0		0			0
Gross Unrealized Losses	[2]	0		0			0
Other Short-term Investments	[2],[3]	79,600,000		79,600,000			214,700,000
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,248,700,000		1,248,700,000			1,192,500,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,248,700,000		1,248,700,000			1,192,500,000
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				122,700,000			61,500,000
Other-Than-Temporary Impairments				(7,600,000)			(7,900,000)
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost	[4]	127,900,000		127,900,000			123,200,000
Gross Unrealized Gains	[4]	2,900,000		2,900,000			100,000
Gross Unrealized Losses	[4]	0		0			0
Other Short-term Investments	[4]	130,800,000		130,800,000			123,300,000
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,793,500,000		1,793,500,000			1,767,900,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	1,793,500,000		1,793,500,000			1,767,900,000
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains	[6]			1,165,800,000			1,144,400,000
Other-Than-Temporary Impairments				0			0
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		30,200,000		30,200,000			29,200,000
Gross Unrealized Gains		22,500,000		22,500,000			21,300,000
Gross Unrealized Losses		0		0			0
Other Short-term Investments	[5]	52,700,000		52,700,000			50,500,000
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	33,700,000		33,700,000			15,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	33,700,000		33,700,000			15,300,000
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		1,039,200,000		1,039,200,000			1,112,500,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,039,200,000		1,039,200,000			1,112,500,000
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				112,300,000			55,500,000
Other-Than-Temporary Impairments				(5,800,000)			(6,100,000)
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		85,600,000		85,600,000			72,400,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		85,600,000		85,600,000			72,400,000
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				8,900,000			5,300,000
Other-Than-Temporary Impairments				(1,500,000)			(1,600,000)
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		123,900,000		123,900,000			7,600,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		123,900,000		123,900,000			7,600,000
State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				1,500,000			700,000
Other-Than-Temporary Impairments				(300,000)			(200,000)
AEP Texas Inc. [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,854,700,000		4,854,700,000			4,558,400,000
Long Term Debt, Fair Value		5,590,000,000.0		5,590,000,000.0			4,981,500,000
AEP Transmission Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,947,900,000		3,947,900,000			3,427,300,000
Long Term Debt, Fair Value		4,859,500,000		4,859,500,000			3,868,000,000.0
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,833,300,000		4,833,300,000			4,363,800,000
Long Term Debt, Fair Value		6,167,600,000		6,167,600,000			5,253,100,000
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,981,900,000		2,981,900,000			3,050,200,000
Long Term Debt, Fair Value		3,637,400,000		3,637,400,000			3,453,800,000
Nuclear Trust Fund Investments
Fair Value		3,075,900,000		3,075,900,000			2,975,700,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		3,075,900,000		3,075,900,000			2,975,700,000
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities				1,200,000,000			1,100,000,000
Nuclear Trust Fund Investments
Gross Unrealized Gains				1,288,500,000			1,205,900,000
Other-Than-Temporary Impairments				(7,600,000)			(7,900,000)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		316,600,000	671,900,000	1,257,100,000		871,400,000
Purchases of Investments		318,600,000	689,100,000	1,290,000,000.0		915,700,000
Gross Realized Gains on Investment Sales		3,400,000	10,900,000	25,400,000		26,600,000
Gross Realized Losses on Investment Sales		500,000	$ 7,100,000	25,200,000		$ 15,100,000
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		291,600,000		291,600,000
After 1 year through 5 years		355,900,000		355,900,000
After 5 years through 10 years		255,100,000		255,100,000
After 10 years		346,100,000		346,100,000
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,100,000,000		1,100,000,000			1,100,000,000
Adjusted Cost of Domestic Equity Securities		628,000,000		628,000,000			623,000,000
Unrealized Loss on Securities				17,000,000			5,000,000
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,248,700,000		1,248,700,000			1,192,500,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,248,700,000		1,248,700,000			1,192,500,000
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				122,700,000			61,500,000
Other-Than-Temporary Impairments				(7,600,000)			(7,900,000)
Indiana Michigan Power Co [Member] | Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,793,500,000		1,793,500,000			1,767,900,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	1,793,500,000		1,793,500,000			1,767,900,000
Indiana Michigan Power Co [Member] | Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				1,165,800,000	[6]		1,144,400,000
Other-Than-Temporary Impairments				0			0
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	33,700,000		33,700,000			15,300,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	33,700,000		33,700,000			15,300,000
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		1,039,200,000		1,039,200,000			1,112,500,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,039,200,000		1,039,200,000			1,112,500,000
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				112,300,000			55,500,000
Other-Than-Temporary Impairments				(5,800,000)			(6,100,000)
Indiana Michigan Power Co [Member] | Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		85,600,000		85,600,000			72,400,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		85,600,000		85,600,000			72,400,000
Indiana Michigan Power Co [Member] | Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				8,900,000			5,300,000
Other-Than-Temporary Impairments				(1,500,000)			(1,600,000)
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		123,900,000		123,900,000			7,600,000
Contractual Maturities, Fair Value of Debt Securities
Fair Value		123,900,000		123,900,000			7,600,000
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains				1,500,000			700,000
Other-Than-Temporary Impairments				(300,000)			(200,000)
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,429,900,000		2,429,900,000			2,082,000,000.0
Long Term Debt, Fair Value		3,137,500,000		3,137,500,000			2,554,300,000
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,373,700,000		1,373,700,000			1,386,200,000
Long Term Debt, Fair Value		1,694,900,000		1,694,900,000			1,603,300,000
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,637,300,000		2,637,300,000			2,655,600,000
Long Term Debt, Fair Value		3,119,200,000		3,119,200,000			2,927,900,000
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			$ 871,000,000

[1] The fair value amounts include debt related to AEP’s Equity Units and had a fair value of $1.6 billion and $871 million as of September 30, 2020 and December 31, 2019, 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 $1.2 billion and $1.1 billion and unrealized losses of $17 million and $5 million as of September 30, 2020 and December 31, 2019, respectively.

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