Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		$ 19,543.7		$ 19,543.7		$ 19,572.7
Long Term Debt, Fair Value		22,443.2		22,443.2		21,201.3
Other Temporary Investments
Cost		294.3		294.3		375.8
Gross Unrealized Gains		12.6		12.6		11.7
Gross Unrealized Losses		0.0		0.0		(0.7)
Fair Value		306.9		306.9		386.8
Debt and Equity Securities Within Other Temporary Investments
Proceeds from Investment Sales		0.0	$ 0.0	0.0	$ 0.0
Purchases of Investments		0.6	0.4	1.0	0.8
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		2,196.0		2,196.0		2,106.4
Gross Unrealized Gains		674.9		674.9		611.8
Other-Than-Temporary Impairments		(81.9)		(81.9)		(83.3)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		639.3	287.6	1,777.0	515.8
Purchases of Investments		644.8	294.9	1,796.4	540.7
Gross Realized Gains on Investment Sales		12.2	7.6	28.0	18.8
Gross Realized Losses on Investment Sales		7.9	5.9	15.7	9.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,196.0		2,196.0		2,106.4
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		927.0		927.0		771.0
Adjusted Cost of Domestic Equity Securities		576.0		576.0		555.0
Appalachian Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		4,044.5		4,044.5		3,930.7
Long Term Debt, Fair Value		4,910.6		4,910.6		4,416.7
Indiana Michigan Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,430.3		2,430.3		2,000.0
Long Term Debt, Fair Value		2,745.8		2,745.8		2,193.6
Nuclear Trust Fund Investments
Fair Value		2,196.0		2,196.0		2,106.4
Gross Unrealized Gains		674.9		674.9		611.8
Other-Than-Temporary Impairments		(81.9)		(81.9)		(83.3)
Securities Activity Within Decommissioning and SNF Trusts
Proceeds from Investment Sales		639.3	287.6	1,777.0	515.8
Purchases of Investments		644.8	294.9	1,796.4	540.7
Gross Realized Gains on Investment Sales		12.2	7.6	28.0	18.8
Gross Realized Losses on Investment Sales		7.9	$ 5.9	15.7	$ 9.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		2,196.0		2,196.0		2,106.4
Fair Value Measurements (Textuals)
Adjusted Cost of Debt Securities		927.0		927.0		771.0
Adjusted Cost of Domestic Equity Securities		576.0		576.0		555.0
Ohio Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,786.0		1,786.0		2,157.7
Long Term Debt, Fair Value		2,220.0		2,220.0		2,472.7
Public Service Co Of Oklahoma [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		1,286.4		1,286.4		1,286.1
Long Term Debt, Fair Value		1,481.8		1,481.8		1,402.9
Southwestern Electric Power Co [Member]
Book Values and Fair Values of Long - term Debt
Total Long-term Debt Outstanding		2,272.8		2,272.8		2,273.5
Long Term Debt, Fair Value		2,555.0		2,555.0		2,417.2
Cash [Member]
Other Temporary Investments
Cost	[1]	188.5		188.5		271.0
Gross Unrealized Gains	[1]	0.0		0.0		0.0
Gross Unrealized Losses	[1]	0.0		0.0		0.0
Fair Value	[1],[2]	188.5		188.5		271.0
Fixed Income Funds [Member]
Nuclear Trust Fund Investments
Fair Value		995.9		995.9		811.2
Gross Unrealized Gains		69.4		69.4		40.2
Other-Than-Temporary Impairments		(3.8)		(3.8)		(4.0)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		995.9		995.9		811.2
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		995.9		995.9		811.2
Gross Unrealized Gains		69.4		69.4		40.2
Other-Than-Temporary Impairments		(3.8)		(3.8)		(4.0)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		995.9		995.9		811.2
Mutual Funds Fixed Income [Member]
Other Temporary Investments
Cost		91.8		91.8		91.1
Gross Unrealized Gains		0.5		0.5		0.0
Gross Unrealized Losses		0.0		0.0		(0.7)
Fair Value		92.3		92.3		90.4
Domestic [Member]
Nuclear Trust Fund Investments
Fair Value	[3]	1,181.5		1,181.5		1,126.9
Gross Unrealized Gains		605.5		605.5		571.6
Other-Than-Temporary Impairments		(78.1)		(78.1)		(79.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[3]	1,181.5		1,181.5		1,126.9
Domestic [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[3]	1,181.5		1,181.5		1,126.9
Gross Unrealized Gains		605.5		605.5		571.6
Other-Than-Temporary Impairments		(78.1)		(78.1)		(79.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities	[3]	1,181.5		1,181.5		1,126.9
Mutual Funds Equity [Member]
Other Temporary Investments
Cost		14.0		14.0		13.7
Gross Unrealized Gains		12.1		12.1		11.7
Gross Unrealized Losses		0.0		0.0		0.0
Fair Value	[3]	26.1		26.1		25.4
Cash and Cash Equivalents [Member]
Nuclear Trust Fund Investments
Fair Value	[4]	18.6		18.6		168.3
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	[4]	18.6		18.6		168.3
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value	[4]	18.6		18.6		168.3
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	[4]	18.6		18.6		168.3
US Government Agencies Debt Securities [Member]
Nuclear Trust Fund Investments
Fair Value		748.9		748.9		731.1
Gross Unrealized Gains		62.2		62.2		35.9
Other-Than-Temporary Impairments		(2.1)		(2.1)		(2.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		748.9		748.9		731.1
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		748.9		748.9		731.1
Gross Unrealized Gains		62.2		62.2		35.9
Other-Than-Temporary Impairments		(2.1)		(2.1)		(2.6)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		748.9		748.9		731.1
Corporate Debt [Member]
Nuclear Trust Fund Investments
Fair Value		66.0		66.0		57.9
Gross Unrealized Gains		6.3		6.3		3.2
Other-Than-Temporary Impairments		(1.0)		(1.0)		(1.1)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		66.0		66.0		57.9
Corporate Debt [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		66.0		66.0		57.9
Gross Unrealized Gains		6.3		6.3		3.2
Other-Than-Temporary Impairments		(1.0)		(1.0)		(1.1)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		66.0		66.0		57.9
State and Local Jurisdiction [Member]
Nuclear Trust Fund Investments
Fair Value		181.0		181.0		22.2
Gross Unrealized Gains		0.9		0.9		1.1
Other-Than-Temporary Impairments		(0.7)		(0.7)		(0.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		181.0		181.0		22.2
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		181.0		181.0		22.2
Gross Unrealized Gains		0.9		0.9		1.1
Other-Than-Temporary Impairments		(0.7)		(0.7)		(0.3)
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		181.0		181.0		$ 22.2
Within One Year [Member]
Nuclear Trust Fund Investments
Fair Value		169.7		169.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		169.7		169.7
Within One Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		169.7		169.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		169.7		169.7
One Year To Five Year [Member]
Nuclear Trust Fund Investments
Fair Value		378.2		378.2
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		378.2		378.2
One Year To Five Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		378.2		378.2
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		378.2		378.2
Five Year To Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		193.3		193.3
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		193.3		193.3
Five Year To Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		193.3		193.3
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		193.3		193.3
After Ten Year [Member]
Nuclear Trust Fund Investments
Fair Value		254.7		254.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		254.7		254.7
After Ten Year [Member] | Indiana Michigan Power Co [Member]
Nuclear Trust Fund Investments
Fair Value		254.7		254.7
Contractual Maturities, Fair Value of Debt Securities
Contractual Maturities, Fair Value of Debt Securities		$ 254.7		$ 254.7

[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.