Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 19,236.4		$ 20,256.4
Long Term Debt, Fair Value		21,239.5
Other Temporary Investments
Cost		260.3		318.8
Gross Unrealized Gains		15.5		13.9
Gross Unrealized Losses		(0.8)		(1.0)
Fair Value		275.0		331.7
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		0.0	$ 0.0
Purchases of Investments		0.5	0.4
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		2,333.2		2,256.2
Gross Unrealized Gains		771.7		707.7
Other-Than-Temporary Impairments		(85.7)		(87.2)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		487.9	1,137.7
Purchases of Investments		505.5	1,151.6
Gross Realized Gains on Investment Sales		11.3	15.8
Gross Realized Losses on Investment Sales		8.1	7.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,333.2		2,256.2
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		21,239.5
Adjusted Cost of Debt Securities		942.0		938.0
Adjusted Cost of Domestic Equity Securities		603.0		592.0
Includes Debt Included In Liabilities Held For Sale [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding	[1]			20,391.2
Long Term Debt, Fair Value	[1]			22,211.9
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value	[1]			22,211.9
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
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,918.8		4,033.9
Long Term Debt, Fair Value		4,558.8		4,613.2
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		4,558.8		4,613.2
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,439.5		2,471.4
Long Term Debt, Fair Value		2,646.8		2,661.6
Nuclear Trust Fund Investments
Fair Value		2,333.2		2,256.2
Gross Unrealized Gains		771.7		707.7
Other-Than-Temporary Impairments		(85.7)		(87.2)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		487.9	1,137.7
Purchases of Investments		505.5	1,151.6
Gross Realized Gains on Investment Sales		11.3	15.8
Gross Realized Losses on Investment Sales		8.1	$ 7.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,333.2		2,256.2
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		2,646.8		2,661.6
Adjusted Cost of Debt Securities		942.0		938.0
Adjusted Cost of Domestic Equity Securities		603.0		592.0
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,742.0		1,763.9
Long Term Debt, Fair Value		2,070.8		2,092.5
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		2,070.8		2,092.5
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,286.1		1,286.0
Long Term Debt, Fair Value		1,431.1		1,419.0
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		1,431.1		1,419.0
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,427.7		2,679.1
Long Term Debt, Fair Value		2,591.2		2,814.3
Fair Value Measurements (Textuals)
Long Term Debt, Fair Value		2,591.2		2,814.3
Cash [Member]
Other Temporary Investments
Cost	[2]	152.7		211.7
Gross Unrealized Gains	[2]	0.0		0.0
Gross Unrealized Losses	[2]	0.0		0.0
Fair Value	[2],[3]	152.7		211.7
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		973.3		967.4
Gross Unrealized Gains		31.1		29.8
Other-Than-Temporary Impairments		(6.8)		(7.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		973.3		967.4
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		973.3		967.4
Gross Unrealized Gains		31.1		29.8
Other-Than-Temporary Impairments		(6.8)		(7.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		973.3		967.4
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost	[4]	93.1		92.7
Gross Unrealized Gains	[4]	0.0		0.0
Gross Unrealized Losses	[4]	(0.8)		(1.0)
Fair Value	[4]	92.3		91.7
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,343.3		1,270.1
Gross Unrealized Gains		740.6		677.9
Other-Than-Temporary Impairments		(78.9)		(79.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[5]	1,343.3		1,270.1
Domestic [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[5]	1,343.3		1,270.1
Gross Unrealized Gains		740.6		677.9
Other-Than-Temporary Impairments		(78.9)		(79.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[5]	1,343.3		1,270.1
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		14.5		14.4
Gross Unrealized Gains		15.5		13.9
Gross Unrealized Losses		0.0		0.0
Fair Value	[5]	30.0		28.3
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[6]	16.6		18.7
Gross Unrealized Gains		0.0		0.0
Other-Than-Temporary Impairments		0.0		0.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[6]	16.6		18.7
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[6]	16.6		18.7
Gross Unrealized Gains		0.0		0.0
Other-Than-Temporary Impairments		0.0		0.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[6]	16.6		18.7
US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		814.2		785.4
Gross Unrealized Gains		28.4		27.1
Other-Than-Temporary Impairments		(4.6)		(5.5)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		814.2		785.4
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		814.2		785.4
Gross Unrealized Gains		28.4		27.1
Other-Than-Temporary Impairments		(4.6)		(5.5)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		814.2		785.4
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		57.2		60.9
Gross Unrealized Gains		2.5		2.3
Other-Than-Temporary Impairments		(1.2)		(1.4)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		57.2		60.9
Corporate Debt [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		57.2		60.9
Gross Unrealized Gains		2.5		2.3
Other-Than-Temporary Impairments		(1.2)		(1.4)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		57.2		60.9
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		101.9		121.1
Gross Unrealized Gains		0.2		0.4
Other-Than-Temporary Impairments		(1.0)		(0.7)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		101.9		121.1
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		101.9		121.1
Gross Unrealized Gains		0.2		0.4
Other-Than-Temporary Impairments		(1.0)		(0.7)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		101.9		$ 121.1
Within One Year [Member]
Nuclear Trust Fund Investments
Fair Value		221.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		221.8
Within One Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		221.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		221.8
One Year To Five Year [Member]
Nuclear Trust Fund Investments
Fair Value		346.3
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		346.3
One Year To Five Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		346.3
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		346.3
Five Year To Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		192.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		192.8
Five Year To Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		192.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		192.8
After Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		212.4
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		212.4
After Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		212.4
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		$ 212.4

[1] Amount includes 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.(b)Primarily short and intermediate maturities which may be sold and do not contain maturity dates.

[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.