Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended			12 Months Ended
		Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018	Dec. 31, 2018
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 25,881.2			$ 25,881.2			$ 23,346.7
Long Term Debt, Fair Value		29,729.1	[1]		29,729.1	[1]		24,093.9
Other Temporary Investments
Cost		322.0			322.0			355.0
Gross Unrealized Gains		17.6			17.6			16.4
Gross Unrealized Losses		(0.2)			(0.2)			(2.3)
Other Short-term Investments		339.4			339.4			369.1
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		2.8		$ 0.0	2.8		$ 0.0
Purchases of Investments		26.9		0.8	35.8		2.2
Gross Realized Gains on Investment Sales		0.0		0.0	0.0		0.0
Gross Realized Losses on Investment Sales		0.0		0.0	0.0		0.0
Nuclear Trust Fund Investments
Fair Value		2,835.2			2,835.2			2,474.9
Contractual Maturities, Fair Value of Debt Securities
Fair Value		2,835.2			2,835.2			2,474.9
Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities					1,000.0			784.0
Nuclear Trust Fund Investments
Gross Unrealized Gains					1,112.3			794.7
Other-Than-Temporary Impairments					(7.7)			(9.2)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		671.9		513.1	871.4		1,550.9
Purchases of Investments		689.1		521.2	915.7		1,589.0
Gross Realized Gains on Investment Sales		10.9		3.9	26.6		27.7
Gross Realized Losses on Investment Sales		7.1		3.5	15.1		22.2
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		334.9			334.9
After 1 year through 5 years		390.9			390.9
After 5 years through 10 years		199.2			199.2
After 10 years		198.5			198.5
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,000.0			1,000.0			1,000.0
Adjusted Cost of Domestic Equity Securities		657.0			657.0			629.0
Unrealized Loss on Securities					9.0			18.0
Cash [Member]
Other Temporary Investments
Cost	[2]	160.1			160.1			230.6
Gross Unrealized Gains	[2]	0.0			0.0			0.0
Gross Unrealized Losses	[2]	0.0			0.0			0.0
Other Short-term Investments	[2],[3]	160.1			160.1			230.6
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,123.5			1,123.5			1,057.1
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,123.5			1,123.5			1,057.1
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					74.6			28.4
Other-Than-Temporary Impairments					(7.7)			(9.2)
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost	[4]	133.4			133.4			106.6
Gross Unrealized Gains	[4]	0.0			0.0			0.0
Gross Unrealized Losses	[4]	(0.2)			(0.2)			(2.3)
Other Short-term Investments	[4]	133.2			133.2			104.3
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,694.3			1,694.3			1,395.3
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	1,694.3			1,694.3			1,395.3
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains	[6]				1,037.7			766.3
Other-Than-Temporary Impairments	[6]				0.0			0.0
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		28.5			28.5			17.8
Gross Unrealized Gains		17.6			17.6			16.4
Gross Unrealized Losses		0.0			0.0			0.0
Other Short-term Investments	[5]	46.1			46.1			34.2
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	17.4			17.4			22.5
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	17.4			17.4			22.5
Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					0.0			0.0
Other-Than-Temporary Impairments					0.0			0.0
US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		1,047.4			1,047.4			996.1
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,047.4			1,047.4			996.1
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					67.8			26.7
Other-Than-Temporary Impairments					(5.8)			(7.1)
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		68.6			68.6			52.4
Contractual Maturities, Fair Value of Debt Securities
Fair Value		68.6			68.6			52.4
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					6.1			1.1
Other-Than-Temporary Impairments					(1.7)			(1.9)
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		7.5			7.5			8.6
Contractual Maturities, Fair Value of Debt Securities
Fair Value		7.5			7.5			8.6
State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					0.7			0.6
Other-Than-Temporary Impairments					(0.2)			(0.2)
AEP Texas Inc. [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,146.5			4,146.5			3,881.3
Long Term Debt, Fair Value		4,631.5			4,631.5			3,964.6
AEP Transmission Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,511.9			3,511.9			2,823.0
Long Term Debt, Fair Value		3,984.9			3,984.9			2,782.4
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,362.9			4,362.9			4,062.6
Long Term Debt, Fair Value		5,370.2			5,370.2			4,473.3
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,031.5			3,031.5			3,035.4
Long Term Debt, Fair Value		3,497.3			3,497.3			3,070.2
Nuclear Trust Fund Investments
Fair Value		2,835.2			2,835.2			2,474.9
Contractual Maturities, Fair Value of Debt Securities
Fair Value		2,835.2			2,835.2			2,474.9
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Unrealized Gain on Securities					1,000.0			784.0
Nuclear Trust Fund Investments
Gross Unrealized Gains					1,112.3			794.7
Other-Than-Temporary Impairments					(7.7)			(9.2)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		671.9		513.1	871.4		1,550.9
Purchases of Investments		689.1		521.2	915.7		1,589.0
Gross Realized Gains on Investment Sales		10.9		3.9	26.6		27.7
Gross Realized Losses on Investment Sales		7.1		$ 3.5	15.1		$ 22.2
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		334.9			334.9
After 1 year through 5 years		390.9			390.9
After 5 years through 10 years		199.2			199.2
After 10 years		198.5			198.5
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,000.0			1,000.0			1,000.0
Adjusted Cost of Domestic Equity Securities		657.0			657.0			629.0
Unrealized Loss on Securities					9.0			18.0
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,123.5			1,123.5			1,057.1
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,123.5			1,123.5			1,057.1
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					74.6			28.4
Other-Than-Temporary Impairments					(7.7)			(9.2)
Indiana Michigan Power Co [Member] | Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,694.3			1,694.3			1,395.3
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[5]	1,694.3			1,694.3			1,395.3
Indiana Michigan Power Co [Member] | Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains	[6]				1,037.7			766.3
Other-Than-Temporary Impairments	[6]				0.0			0.0
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[7]	17.4			17.4			22.5
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[7]	17.4			17.4			22.5
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			0.0
Other-Than-Temporary Impairments					0.0			0.0
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		1,047.4			1,047.4			996.1
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,047.4			1,047.4			996.1
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					67.8			26.7
Other-Than-Temporary Impairments					(5.8)			(7.1)
Indiana Michigan Power Co [Member] | Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		68.6			68.6			52.4
Contractual Maturities, Fair Value of Debt Securities
Fair Value		68.6			68.6			52.4
Indiana Michigan Power Co [Member] | Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					6.1			1.1
Other-Than-Temporary Impairments					(1.7)			(1.9)
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		7.5			7.5			8.6
Contractual Maturities, Fair Value of Debt Securities
Fair Value		7.5			7.5			8.6
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains					0.7			0.6
Other-Than-Temporary Impairments					(0.2)			(0.2)
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,113.9			2,113.9			1,716.6
Long Term Debt, Fair Value		2,618.5			2,618.5			1,919.7
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,386.4			1,386.4			1,287.0
Long Term Debt, Fair Value		1,632.9			1,632.9			1,361.9
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,656.9			2,656.9			2,713.4
Long Term Debt, Fair Value		2,983.0			2,983.0			$ 2,670.2
Equity Units [Member]
Book Values and Fair Values of Long - term Debt
Long Term Debt, Fair Value		$ 887.0			$ 887.0

[1] The fair value amount includes debt related to AEP’s Equity Units issued in March 2019 and has a fair value of $887 million as of September 30, 2019. See “Equity Units” section of Note 13 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 billion and $784 million and unrealized losses of $9 million and $18 million as of September 30, 2019 and December 31, 2018, respectively. AEP adopted ASU 2016-01 during the first quarter of 2018 by means of a modified retrospective approach. Due to the adoption of the ASU, Other-Than-Temporary Impairments are no longer applicable to Equity Securities with readily determinable fair values.

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