Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 19,782.6		$ 19,572.7
Long Term Debt, Fair Value		22,052.8		21,201.3
Other Temporary Investments
Cost		252.7		375.8
Gross Unrealized Gains		11.8		11.7
Gross Unrealized Losses		0.0		(0.7)
Estimated Fair Value		264.5		386.8
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		0.0	$ 0.0
Purchases of Investments		0.4	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		2,152.4		2,106.4
Gross Unrealized Gains		641.9		611.8
Other-Than-Temporary Impairments		(82.3)		(83.3)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		1,137.7	228.2
Purchases of Investments		1,151.6	245.8
Gross Realized Gains on Investment Sales		15.8	11.2
Gross Realized Losses on Investment Sales		7.8	3.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,152.4		2,106.4
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		801.0		771.0
Adjusted Cost of Domestic Equity Securities		568.0		555.0
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		3,919.3		3,930.7
Long Term Debt, Fair Value		4,597.8		4,416.7
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,366.6		2,000.0
Long Term Debt, Fair Value		2,595.4		2,193.6
Nuclear Trust Fund Investments
Fair Value		2,152.4		2,106.4
Gross Unrealized Gains		641.9		611.8
Other-Than-Temporary Impairments		(82.3)		(83.3)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		1,137.7	228.2
Purchases of Investments		1,151.6	245.8
Gross Realized Gains on Investment Sales		15.8	11.2
Gross Realized Losses on Investment Sales		7.8	$ 3.8
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,152.4		2,106.4
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		801.0		771.0
Adjusted Cost of Domestic Equity Securities		568.0		555.0
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,135.5		2,157.7
Long Term Debt, Fair Value		2,515.4		2,472.7
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,286.3		1,286.1
Long Term Debt, Fair Value		1,463.6		1,402.9
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,272.4		2,273.5
Long Term Debt, Fair Value		2,483.4		2,417.2
Cash [Member]
Other Temporary Investments
Cost	[1]	147.4		271.0
Gross Unrealized Gains	[1]	0.0		0.0
Gross Unrealized Losses	[1]	0.0		0.0
Estimated Fair Value	[1],[2]	147.4		271.0
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		859.0		811.2
Gross Unrealized Gains		58.4		40.2
Other-Than-Temporary Impairments		(3.4)		(4.0)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		859.0		811.2
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		859.0		811.2
Gross Unrealized Gains		58.4		40.2
Other-Than-Temporary Impairments		(3.4)		(4.0)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		859.0		811.2
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost		91.4		91.1
Gross Unrealized Gains		0.1		0.0
Gross Unrealized Losses		0.0		(0.7)
Estimated Fair Value		91.5		90.4
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[3]	1,151.4		1,126.9
Gross Unrealized Gains		583.5		571.6
Other-Than-Temporary Impairments		(78.9)		(79.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[3]	1,151.4		1,126.9
Domestic [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[3]	1,151.4		1,126.9
Gross Unrealized Gains		583.5		571.6
Other-Than-Temporary Impairments		(78.9)		(79.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[3]	1,151.4		1,126.9
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		13.9		13.7
Gross Unrealized Gains		11.7		11.7
Gross Unrealized Losses		0.0		0.0
Estimated Fair Value	[3]	25.6		25.4
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[4]	142.0		168.3
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	[4]	142.0		168.3
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[4]	142.0		168.3
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	[4]	142.0		168.3
US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		761.1		731.1
Gross Unrealized Gains		52.3		35.9
Other-Than-Temporary Impairments		(2.1)		(2.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		761.1		731.1
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		761.1		731.1
Gross Unrealized Gains		52.3		35.9
Other-Than-Temporary Impairments		(2.1)		(2.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		761.1		731.1
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		68.9		57.9
Gross Unrealized Gains		4.9		3.2
Other-Than-Temporary Impairments		(1.0)		(1.1)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		68.9		57.9
Corporate Debt [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		68.9		57.9
Gross Unrealized Gains		4.9		3.2
Other-Than-Temporary Impairments		(1.0)		(1.1)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		68.9		57.9
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		29.0		22.2
Gross Unrealized Gains		1.2		1.1
Other-Than-Temporary Impairments		(0.3)		(0.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		29.0		22.2
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		29.0		22.2
Gross Unrealized Gains		1.2		1.1
Other-Than-Temporary Impairments		(0.3)		(0.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		29.0		$ 22.2
Within One Year [Member]
Nuclear Trust Fund Investments
Fair Value		175.4
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		175.4
Within One Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		175.4
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		175.4
One Year To Five Year [Member]
Nuclear Trust Fund Investments
Fair Value		369.6
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		369.6
One Year To Five Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		369.6
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		369.6
Five Year To Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		133.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		133.0
Five Year To Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		133.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		133.0
After Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		181.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		181.0
After Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		181.0
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		$ 181.0

[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 with third parties. Level 1 and Level 2 amounts primarily represent investments in money market funds.

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

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