Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
		Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 21,461.0			$ 21,173.3
Long Term Debt, Fair Value		23,039.8			23,649.6
Other Temporary Investments
Cost		284.0			341.4
Gross Unrealized Gains		19.2			19.7
Gross Unrealized Losses		(2.2)			(1.4)
Fair Value		301.0			359.7
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		0.0		$ 0.0
Purchases of Investments		0.6		0.5
Gross Realized Gains on Investment Sales		0.0		0.0
Gross Realized Losses on Investment Sales		0.0		0.0
Nuclear Trust Fund Investments
Fair Value		2,510.6			2,527.6
Contractual Maturities, Fair Value of Debt Securities
Fair Value		2,510.6			2,527.6
Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		871.9			902.5
Other-Than-Temporary Impairments		(10.3)			(80.5)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		508.6		487.9
Purchases of Investments		525.3		505.5
Gross Realized Gains on Investment Sales		12.0		11.3
Gross Realized Losses on Investment Sales		10.9		8.1
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		355.7
After 1 year through 5 years		315.3
After 5 years through 10 years		205.8
After 10 years		164.2
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,000.0			1,000.0
Adjusted Cost of Domestic Equity Securities		603.0			594.0
AEP Texas Inc. [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,553.3			3,649.3
Long Term Debt, Fair Value		3,818.3			3,964.8
AEP Transmission Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,550.7			2,550.4
Long Term Debt, Fair Value		2,620.6			2,782.9
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,969.3			3,980.1
Long Term Debt, Fair Value		4,532.0			4,782.6
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,717.2			2,745.1
Long Term Debt, Fair Value		2,869.5			3,014.7
Nuclear Trust Fund Investments
Fair Value		2,510.6			2,527.6
Contractual Maturities, Fair Value of Debt Securities
Fair Value		2,510.6			2,527.6
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		871.9			902.5
Other-Than-Temporary Impairments		(10.3)			(80.5)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		508.6		487.9
Purchases of Investments		525.3		505.5
Gross Realized Gains on Investment Sales		12.0		11.3
Gross Realized Losses on Investment Sales		10.9		$ 8.1
Contractual Maturities, Fair Value of Debt Securities
Within 1 year		355.7
After 1 year through 5 years		315.3
After 5 years through 10 years		205.8
After 10 years		164.2
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		1,000.0			1,000.0
Adjusted Cost of Domestic Equity Securities		603.0			594.0
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,089.7			1,719.3
Long Term Debt, Fair Value		2,367.9			2,064.3
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,286.7			1,286.5
Long Term Debt, Fair Value		1,400.3			1,457.1
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,503.7			2,441.9
Long Term Debt, Fair Value		2,587.3			2,645.9
Cash [Member]
Other Temporary Investments
Cost	[1]	162.0			220.1
Gross Unrealized Gains	[1]	0.0			0.0
Gross Unrealized Losses	[1]	0.0			0.0
Fair Value	[1],[2]	162.0			220.1
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,041.0			1,048.7
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,041.0			1,048.7
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		21.6			34.3
Other-Than-Temporary Impairments		(10.3)			(5.0)
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		1,041.0			1,048.7
Contractual Maturities, Fair Value of Debt Securities
Fair Value		1,041.0			1,048.7
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		21.6			34.3
Other-Than-Temporary Impairments		(10.3)			(5.0)
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost	[3]	104.8			104.3
Gross Unrealized Gains	[3]	0.0			0.0
Gross Unrealized Losses	[3]	(2.2)			(1.4)
Fair Value	[3]	102.6			102.9
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[4]	1,453.2			1,461.7
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[4]	1,453.2			1,461.7
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		850.3			868.2
Other-Than-Temporary Impairments		0.0	[5]		(75.5)
Unrealized Gain on Securities		855.0
Unrealized Loss on Securities		4.7
Domestic [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[4]	1,453.2			1,461.7
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[4]	1,453.2			1,461.7
Domestic [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		850.3			868.2
Other-Than-Temporary Impairments		0.0			(75.5)
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		17.2			17.0
Gross Unrealized Gains		19.2			19.7
Gross Unrealized Losses		0.0			0.0
Fair Value	[4]	36.4			36.7
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[6]	16.4			17.2
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[6]	16.4			17.2
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
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[6]	16.4			17.2
Contractual Maturities, Fair Value of Debt Securities
Fair Value	[6]	16.4			17.2
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [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		974.6			981.2
Contractual Maturities, Fair Value of Debt Securities
Fair Value		974.6			981.2
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		19.0			29.7
Other-Than-Temporary Impairments		(8.4)			(3.6)
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		974.6			981.2
Contractual Maturities, Fair Value of Debt Securities
Fair Value		974.6			981.2
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		19.0			29.7
Other-Than-Temporary Impairments		(8.4)			(3.6)
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		57.8			58.7
Contractual Maturities, Fair Value of Debt Securities
Fair Value		57.8			58.7
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		2.0			3.8
Other-Than-Temporary Impairments		(1.7)			(1.2)
Corporate Debt [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		57.8			58.7
Contractual Maturities, Fair Value of Debt Securities
Fair Value		57.8			58.7
Corporate Debt [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		2.0			3.8
Other-Than-Temporary Impairments		(1.7)			(1.2)
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		8.6			8.8
Contractual Maturities, Fair Value of Debt Securities
Fair Value		8.6			8.8
State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		0.6			0.8
Other-Than-Temporary Impairments		(0.2)			(0.2)
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		8.6			8.8
Contractual Maturities, Fair Value of Debt Securities
Fair Value		8.6			8.8
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]
Nuclear Trust Fund Investments
Gross Unrealized Gains		0.6			0.8
Other-Than-Temporary Impairments		$ (0.2)			$ (0.2)

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

[2] 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.

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

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

[5] Amount reported as Gross Unrealized Gains includes unrealized gains of $855 million and unrealized losses of $4.7 million. 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.

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