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Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | $ 41,974,400,000 |  | $ 41,974,400,000 |  | $ 40,143,200,000
Long Term Debt, Fair Value |  | 40,104,200,000 |  | 40,104,200,000 |  | 37,325,700,000
Other Temporary Investments |  |  |  |  |  |
Cost |  | 253,200,000 |  | 253,200,000 |  | 243,500,000
Other Short-term Investments |  | 282,000,000.0 |  | 282,000,000.0 |  | 263,200,000
Debt and Equity Securities Within Other Temporary Investments |  |  |  |  |  |
Proceeds from Investment Sales |  | 4,500,000 | $ 800,000 | 7,500,000 | $ 800,000 |
Purchases of Investments |  | 6,000,000.0 | 14,600,000 | 9,000,000.0 | 16,900,000 |
Gross Realized Gains on Investment Sales |  | 400,000 | 300,000 | 700,000 | 300,000 |
Gross Realized Losses on Investment Sales |  | 300,000 | 0 | 500,000 | 0 |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 4,425,800,000 |  | 4,425,800,000 |  | 3,860,200,000
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Payments to Acquire Investments |  |  |  | 2,398,000,000 | 2,199,700,000 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 4,425,800,000 |  | 4,425,800,000 |  | 3,860,200,000
Gain [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  | 32,200,000 |  | 25,900,000
Loss [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  | (3,400,000) |  | (6,200,000)
Other [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Other Short-term Investments |  | 17,000,000.0 |  | 17,000,000.0 |  | 13,900,000
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Payments to Acquire Investments |  | 1,201,900,000 | 949,500,000 | 2,389,000,000 | 2,182,800,000 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Within 1 year |  | 401,200,000 |  | 401,200,000 |  |
After 1 year through 5 years |  | 600,800,000 |  | 600,800,000 |  |
After 5 years through 10 years |  | 249,700,000 |  | 249,700,000 |  |
After 10 years |  | 336,100,000 |  | 336,100,000 |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Adjusted Cost of Debt Securities |  | 1,500,000,000 |  | 1,500,000,000 |  | 1,400,000,000
Adjusted Cost of Domestic Equity Securities |  | 541,000,000 |  | 541,000,000 |  | 568,000,000
Other than Temporary Impairment Losses, Investments |  |  |  | (19,500,000) |  | (41,800,000)
Proceeds from Sale of Other Investments |  | 1,181,900,000 | 933,000,000.0 | 2,336,000,000 | 2,139,300,000 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (2,200,000) |  | (2,200,000) |  | (10,000,000.0)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 2,320,300,000 |  | 2,320,300,000 |  | 1,902,900,000
Spent Nuclear Fuel and Decommissioning Trusts [Member] | Gain [Member] |  |  |  |  |  |
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Realized Investment Gains (Losses) |  | 108,400,000 | 36,800,000 | 118,700,000 | 91,600,000 |
Spent Nuclear Fuel and Decommissioning Trusts [Member] | Loss [Member] |  |  |  |  |  |
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Gain (Loss) on Investments |  | 700,000 | 7,700,000 | 6,100,000 | 20,000,000.0 |
Cash [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Cost | [1] | 53,400,000 |  | 53,400,000 |  | 48,900,000
Other Short-term Investments | [1] | 53,400,000 |  | 53,400,000 |  | 48,900,000
Cash [Member] | Gain [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments | [1] |  |  | 0 |  | 0
Cash [Member] | Loss [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments | [1] |  |  | 0 |  | 0
Fixed Income Funds [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 1,587,800,000 |  | 1,587,800,000 |  | 1,406,800,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 1,587,800,000 |  | 1,587,800,000 |  | 1,406,800,000
Fixed Income Funds [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | (19,500,000) |  | (41,800,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (1,900,000) |  | (1,900,000) |  | (9,100,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 49,300,000 |  | 49,300,000 |  | 33,400,000
Mutual Funds Fixed Income [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Cost | [2] | 168,000,000.0 |  | 168,000,000.0 |  | 165,900,000
Other Short-term Investments | [2] | 164,600,000 |  | 164,600,000 |  | 159,700,000
Mutual Funds Fixed Income [Member] | Gain [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments | [2] |  |  | 0 |  | 0
Mutual Funds Fixed Income [Member] | Loss [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments | [2] |  |  | (3,400,000) |  | (6,200,000)
Mutual Funds Fixed Income [Member] | Other [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Other Short-term Investments |  | 0 |  | 0 |  | 0
Domestic [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [3] | 2,811,800,000 |  | 2,811,800,000 |  | 2,436,600,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [3] | 2,811,800,000 |  | 2,811,800,000 |  | 2,436,600,000
Domestic [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [3] | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [3] | 0 |  | 0 |  | 0
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (300,000) |  | (300,000) |  | (900,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 2,271,000,000 |  | 2,271,000,000 |  | 1,869,500,000
Mutual Funds Equity [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Cost |  | 14,800,000 |  | 14,800,000 |  | 14,800,000
Other Short-term Investments | [3] | 47,000,000.0 |  | 47,000,000.0 |  | 40,700,000
Mutual Funds Equity [Member] | Gain [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  | 32,200,000 |  | 25,900,000
Mutual Funds Equity [Member] | Loss [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  | 0 |  | 0
Mutual Funds Equity [Member] | Other [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Other Short-term Investments | [3] | 0 |  | 0 |  | 0
Cash and Cash Equivalents [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [4] | 26,200,000 |  | 26,200,000 |  | 16,800,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [4] | 26,200,000 |  | 26,200,000 |  | 16,800,000
Cash and Cash Equivalents [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [4] | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [4] | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0 |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 |  | 0 |  | 0
US Government Agencies Debt Securities [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 1,370,500,000 |  | 1,370,500,000 |  | 1,273,000,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 1,370,500,000 |  | 1,370,500,000 |  | 1,273,000,000
US Government Agencies Debt Securities [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | (22,500,000) |  | (33,200,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (100,000) |  | (100,000) |  | (3,900,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 42,000,000.0 |  | 42,000,000.0 |  | 28,600,000
Corporate Debt [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 215,600,000 |  | 215,600,000 |  | 132,100,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 215,600,000 |  | 215,600,000 |  | 132,100,000
Corporate Debt [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 3,000,000.0 |  | (8,600,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (1,800,000) |  | (1,800,000) |  | (5,200,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 7,300,000 |  | 7,300,000 |  | 4,800,000
State and Local Jurisdiction [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 1,700,000 |  | 1,700,000 |  | 1,700,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 1,700,000 |  | 1,700,000 |  | 1,700,000
State and Local Jurisdiction [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0 |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 |  | 0 |  | 0
Other Cash Deposits [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Cost |  | 17,000,000.0 |  | 17,000,000.0 |  | 13,900,000
Other Short-term Investments |  | 17,000,000.0 |  | 17,000,000.0 |  | 13,900,000
Other Cash Deposits [Member] | Gain [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  | 0 |  | 0
Other Cash Deposits [Member] | Loss [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Unrealized Gain (Loss) on Investments |  |  |  | 0 |  | 0
Other Cash Deposits [Member] | Other [Member] |  |  |  |  |  |
Other Temporary Investments |  |  |  |  |  |
Other Short-term Investments | [5] | 17,000,000.0 |  | 17,000,000.0 |  | 13,900,000
AEP Texas Inc. [Member] |  |  |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | 6,479,400,000 |  | 6,479,400,000 |  | 5,889,800,000
Long Term Debt, Fair Value |  | 6,112,100,000 |  | 6,112,100,000 |  | 5,400,700,000
AEP Transmission Co [Member] |  |  |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | 5,862,300,000 |  | 5,862,300,000 |  | 5,414,400,000
Long Term Debt, Fair Value |  | 5,288,500,000 |  | 5,288,500,000 |  | 4,796,900,000
Appalachian Power Co [Member] |  |  |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | 5,659,200,000 |  | 5,659,200,000 |  | 5,588,300,000
Long Term Debt, Fair Value |  | 5,582,500,000 |  | 5,582,500,000 |  | 5,390,100,000
Indiana Michigan Power Co [Member] |  |  |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | 3,517,500,000 |  | 3,517,500,000 |  | 3,499,400,000
Long Term Debt, Fair Value |  | 3,363,400,000 |  | 3,363,400,000 |  | 3,291,600,000
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 4,425,800,000 |  | 4,425,800,000 |  | 3,860,200,000
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Payments to Acquire Investments |  |  |  | 2,389,000,000 | 2,182,800,000 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 4,425,800,000 |  | 4,425,800,000 |  | 3,860,200,000
Indiana Michigan Power Co [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Payments to Acquire Investments |  | 1,201,900,000 | 949,500,000 | 2,389,000,000 | 2,182,800,000 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Within 1 year |  | 401,200,000 |  | 401,200,000 |  |
After 1 year through 5 years |  | 600,800,000 |  | 600,800,000 |  |
After 5 years through 10 years |  | 249,700,000 |  | 249,700,000 |  |
After 10 years |  | 336,100,000 |  | 336,100,000 |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Adjusted Cost of Debt Securities |  | 1,500,000,000 |  | 1,500,000,000 |  | 1,400,000,000
Adjusted Cost of Domestic Equity Securities |  | 541,000,000 |  | 541,000,000 |  | 568,000,000
Other than Temporary Impairment Losses, Investments |  |  |  | (19,500,000) |  | (41,800,000)
Proceeds from Sale of Other Investments |  | 1,181,900,000 | 933,000,000.0 | 2,336,000,000 | 2,139,300,000 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (2,200,000) |  | (2,200,000) |  | (10,000,000.0)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 2,320,300,000 |  | 2,320,300,000 |  | 1,902,900,000
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] | Gain [Member] |  |  |  |  |  |
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Realized Investment Gains (Losses) |  | 108,400,000 | 36,800,000 | 118,700,000 | 91,600,000 |
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] | Loss [Member] |  |  |  |  |  |
Securities Activity Within Decommissioning and SNF Trusts |  |  |  |  |  |
Gain (Loss) on Investments |  | 700,000 | $ 7,700,000 | 6,100,000 | $ 20,000,000.0 |
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 1,587,800,000 |  | 1,587,800,000 |  | 1,406,800,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 1,587,800,000 |  | 1,587,800,000 |  | 1,406,800,000
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | (19,500,000) |  | (41,800,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (1,900,000) |  | (1,900,000) |  | (9,100,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 49,300,000 |  | 49,300,000 |  | 33,400,000
Indiana Michigan Power Co [Member] | Domestic [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [3] | 2,811,800,000 |  | 2,811,800,000 |  | 2,436,600,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [3] | 2,811,800,000 |  | 2,811,800,000 |  | 2,436,600,000
Indiana Michigan Power Co [Member] | Domestic [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [3] | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [3] | 0 |  | 0 |  | 0
Indiana Michigan Power Co [Member] | Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (300,000) |  | (300,000) |  | (900,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 2,271,000,000 |  | 2,271,000,000 |  | 1,869,500,000
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [4] | 26,200,000 |  | 26,200,000 |  | 16,800,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [4] | 26,200,000 |  | 26,200,000 |  | 16,800,000
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value | [4] | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value | [4] | 10,600,000 |  | 10,600,000 |  | 9,000,000.0
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0 |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 |  | 0 |  | 0
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 1,370,500,000 |  | 1,370,500,000 |  | 1,273,000,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 1,370,500,000 |  | 1,370,500,000 |  | 1,273,000,000
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | (22,500,000) |  | (33,200,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (100,000) |  | (100,000) |  | (3,900,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 42,000,000.0 |  | 42,000,000.0 |  | 28,600,000
Indiana Michigan Power Co [Member] | Corporate Debt [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 215,600,000 |  | 215,600,000 |  | 132,100,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 215,600,000 |  | 215,600,000 |  | 132,100,000
Indiana Michigan Power Co [Member] | Corporate Debt [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Indiana Michigan Power Co [Member] | Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 3,000,000.0 |  | (8,600,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (1,800,000) |  | (1,800,000) |  | (5,200,000)
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 7,300,000 |  | 7,300,000 |  | 4,800,000
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 1,700,000 |  | 1,700,000 |  | 1,700,000
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 1,700,000 |  | 1,700,000 |  | 1,700,000
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member] | Other [Member] |  |  |  |  |  |
Nuclear Trust Fund Investments |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Contractual Maturities, Fair Value of Debt Securities |  |  |  |  |  |
Fair Value |  | 0 |  | 0 |  | 0
Indiana Michigan Power Co [Member] | State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |  |  |
Other than Temporary Impairment Losses, Investments |  |  |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0 |  | 0 |  | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 |  | 0 |  | 0
Ohio Power Co [Member] |  |  |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | 3,715,000,000 |  | 3,715,000,000 |  | 3,366,800,000
Long Term Debt, Fair Value |  | 3,389,600,000 |  | 3,389,600,000 |  | 2,992,100,000
Public Service Co Of Oklahoma [Member] |  |  |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | 2,385,400,000 |  | 2,385,400,000 |  | 2,384,600,000
Long Term Debt, Fair Value |  | 2,210,900,000 |  | 2,210,900,000 |  | 2,154,300,000
Southwestern Electric Power Co [Member] |  |  |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |  |  |
Total Long-term Debt Outstanding |  | 3,648,700,000 |  | 3,648,700,000 |  | 3,646,900,000
Long Term Debt, Fair Value |  | $ 3,329,100,000 |  | $ 3,329,100,000 |  | $ 3,209,700,000
[1] | Primarily represents amounts held for the repayment of debt.
[2] | Primarily short and intermediate maturities which may be sold and do not contain maturity dates.
[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.
[5] | 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.

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