Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 19,551.9		$ 19,551.9		$ 20,256.4
Long Term Debt, Fair Value		21,857.2		21,857.2
Other Temporary Investments
Cost		301.9		301.9		318.8
Gross Unrealized Gains		16.4		16.4		13.9
Gross Unrealized Losses		(0.7)		(0.7)		(1.0)
Fair Value		317.6		317.6		331.7
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		0.0	$ 0.0	0.0	$ 0.0
Purchases of Investments		0.5	0.6	1.0	1.0
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		2,382.0		2,382.0		2,256.2
Gross Unrealized Gains		772.3		772.3		707.7
Other-Than-Temporary Impairments		(382.6)		(382.6)		(87.2)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		801.2	639.3	1,289.1	1,777.0
Purchases of Investments		811.7	644.8	1,317.2	1,796.4
Gross Realized Gains on Investment Sales		177.0	12.2	188.3	28.0
Gross Realized Losses on Investment Sales		132.1	7.9	140.2	15.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,382.0		2,382.0		2,256.2
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		21,857.2		21,857.2
Adjusted Cost of Debt Securities		1,000.0		1,000.0		938.0
Adjusted Cost of Domestic Equity Securities		578.0		578.0		592.0
Lawrenceburg Plant [Member]
Book Values and Fair Values of Long - term Debt
Long Term Debt, Fair Value						172.0
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value						172.0
Includes Debt Included In Liabilities Held For Sale [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		19,551.9		19,551.9		20,391.2	[1]
Long Term Debt, Fair Value	[1]					22,211.9
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value	[1]					22,211.9
AEP Transmission Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,931.4		1,931.4		1,932.0
Long Term Debt, Fair Value		2,105.2		2,105.2		1,984.3
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		2,105.2		2,105.2		1,984.3
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,990.5		3,990.5		4,033.9
Long Term Debt, Fair Value		4,734.5		4,734.5		4,613.2
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		4,734.5		4,734.5		4,613.2
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,691.4		2,691.4		2,471.4
Long Term Debt, Fair Value		2,937.7		2,937.7		2,661.6
Nuclear Trust Fund Investments
Fair Value		2,382.0		2,382.0		2,256.2
Gross Unrealized Gains		772.3		772.3		707.7
Other-Than-Temporary Impairments		(382.6)		(382.6)		(87.2)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		801.2	639.3	1,289.1	1,777.0
Purchases of Investments		811.7	644.8	1,317.2	1,796.4
Gross Realized Gains on Investment Sales		177.0	12.2	188.3	28.0
Gross Realized Losses on Investment Sales		132.1	$ 7.9	140.2	$ 15.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,382.0		2,382.0		2,256.2
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		2,937.7		2,937.7		2,661.6
Adjusted Cost of Debt Securities		1,000.0		1,000.0		938.0
Adjusted Cost of Domestic Equity Securities		578.0		578.0		592.0
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,742.5		1,742.5		1,763.9
Long Term Debt, Fair Value		2,098.7		2,098.7		2,092.5
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		2,098.7		2,098.7		2,092.5
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,286.3		1,286.3		1,286.0
Long Term Debt, Fair Value		1,451.5		1,451.5		1,419.0
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		1,451.5		1,451.5		1,419.0
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,442.7		2,442.7		2,679.1
Long Term Debt, Fair Value		2,634.8		2,634.8		2,814.3
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		2,634.8		2,634.8		2,814.3
Cash [Member]
Other Temporary Investments
Cost	[2]	193.7		193.7		211.7
Gross Unrealized Gains	[2]	0.0		0.0		0.0
Gross Unrealized Losses	[2]	0.0		0.0		0.0
Fair Value	[2],[3]	193.7		193.7		211.7
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		1,049.8		1,049.8		967.4
Gross Unrealized Gains		36.8		36.8		29.8
Other-Than-Temporary Impairments		(306.5)		(306.5)		(7.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		1,049.8		1,049.8		967.4
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		1,049.8		1,049.8		967.4
Gross Unrealized Gains		36.8		36.8		29.8
Other-Than-Temporary Impairments		(306.5)		(306.5)		(7.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		1,049.8		1,049.8		967.4
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost	[4]	93.5		93.5		92.7
Gross Unrealized Gains	[4]	0.0		0.0		0.0
Gross Unrealized Losses	[4]	(0.7)		(0.7)		(1.0)
Fair Value	[4]	92.8		92.8		91.7
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,313.0		1,313.0		1,270.1
Gross Unrealized Gains		735.5		735.5		677.9
Other-Than-Temporary Impairments		(76.1)		(76.1)		(79.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[5]	1,313.0		1,313.0		1,270.1
Domestic [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,313.0		1,313.0		1,270.1
Gross Unrealized Gains		735.5		735.5		677.9
Other-Than-Temporary Impairments		(76.1)		(76.1)		(79.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[5]	1,313.0		1,313.0		1,270.1
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		14.7		14.7		14.4
Gross Unrealized Gains		16.4		16.4		13.9
Gross Unrealized Losses		0.0		0.0		0.0
Fair Value	[5]	31.1		31.1		28.3
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[6]	19.2		19.2		18.7
Gross Unrealized Gains		0.0		0.0		0.0
Other-Than-Temporary Impairments		0.0		0.0		0.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[6]	19.2		19.2		18.7
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[6]	19.2		19.2		18.7
Gross Unrealized Gains		0.0		0.0		0.0
Other-Than-Temporary Impairments		0.0		0.0		0.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[6]	19.2		19.2		18.7
US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		904.1		904.1		785.4
Gross Unrealized Gains		33.5		33.5		27.1
Other-Than-Temporary Impairments		(304.1)		(304.1)		(5.5)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		904.1		904.1		785.4
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		904.1		904.1		785.4
Gross Unrealized Gains		33.5		33.5		27.1
Other-Than-Temporary Impairments		(304.1)		(304.1)		(5.5)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		904.1		904.1		785.4
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		59.0		59.0		60.9
Gross Unrealized Gains		3.3		3.3		2.3
Other-Than-Temporary Impairments		(1.2)		(1.2)		(1.4)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		59.0		59.0		60.9
Corporate Debt [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		59.0		59.0		60.9
Gross Unrealized Gains		3.3		3.3		2.3
Other-Than-Temporary Impairments		(1.2)		(1.2)		(1.4)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		59.0		59.0		60.9
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		86.7		86.7		121.1
Gross Unrealized Gains		0.0		0.0		0.4
Other-Than-Temporary Impairments		(1.2)		(1.2)		(0.7)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		86.7		86.7		121.1
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		86.7		86.7		121.1
Gross Unrealized Gains		0.0		0.0		0.4
Other-Than-Temporary Impairments		(1.2)		(1.2)		(0.7)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		86.7		86.7		$ 121.1
Within One Year [Member]
Nuclear Trust Fund Investments
Fair Value		243.9		243.9
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		243.9		243.9
Within One Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		243.9		243.9
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		243.9		243.9
One Year To Five Year [Member]
Nuclear Trust Fund Investments
Fair Value		398.9		398.9
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		398.9		398.9
One Year To Five Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		398.9		398.9
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		398.9		398.9
Five Year To Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		160.6		160.6
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		160.6		160.6
Five Year To Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		160.6		160.6
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		160.6		160.6
After Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		246.4		246.4
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		246.4		246.4
After Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		246.4		246.4
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		$ 246.4		$ 246.4

[1] Amounts include debt related to the Lawrenceburg Plant that has been classified as Liabilities Held for Sale on the balance sheet and has a fair value of $172 million. See the Assets and Liabilities Held for Sale section of Note 6 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 with 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] Amounts in “Other’’ column primarily represent accrued interest receivables from financial institutions. Level 1 amounts primarily represent investments in money market funds.