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Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | $ 40,143.2 | $ 36,801.0 |
Long-term Debt, Fair Value | [1] | 37,325.7 | 35,915.9 |
Other Temporary Investments |  |  |  |
Cost |  | 243.5 | 223.6 |
Gross Unrealized Gains |  | 25.9 | 19.4 |
Gross Unrealized Losses |  | (6.2) | (8.3) |
Fair Value |  | 263.2 | 234.7 |
Debt and Equity Securities Within Other Temporary Investments |  |  |  |
Proceeds From Investment Sales |  | 7.6 | 30.2 | $ 15.0
Purchases of Investments |  | 18.5 | 18.8 | 26.9
Gross Realized Gains on Investment Sales |  | 1.1 | 6.1 | 3.6
Gross Realized Losses on Investment Sales |  | 0.3 | 1.3 | 0.0
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 3,860.2 | 3,341.2 |
Securities Activity Within the Decommissioning and SNF Trusts |  |  |  |
Payments to Acquire Investments |  | 2,863.6 | 2,784.2 | 1,955.1
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 3,860.2 | 3,341.2 |
Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Securities Activity Within the Decommissioning and SNF Trusts |  |  |  |
Payments to Acquire Investments |  | 2,845.1 | 2,765.4 | 1,928.2
Realized Investment Gains (Losses) |  | 99.0 | 52.4 | 103.2
Gain (Loss) on Investments |  | 26.6 | 42.6 | 16.5
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Within 1 year |  | 359.6 |  |
After 1 year through 5 years |  | 597.6 |  |
After 5 years through 10 years |  | 180.7 |  |
After 10 years |  | 268.9 |  |
Fair Value Measurements (Textuals) |  |  |  |
Adjusted Cost of Debt Securities |  | 1,400.0 | 1,200.0 |
Adjusted Cost of Domestic Equity Securities |  | 568.0 | 654.0 |
Proceeds from Sale of Other Investments |  | 2,787.5 | 2,713.6 | 1,886.4
Realized Investment Gains (Losses) |  | 99.0 | 52.4 | 103.2
Gain (Loss) on Investments |  | 26.6 | 42.6 | 16.5
Other than Temporary Impairment Losses, Investments |  | (41.8) | (28.5) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 1,902.9 | 1,496.3 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (10.0) | (29.0) |
Cash [Member] |  |  |  |
Other Temporary Investments |  |  |  |
Cost | [2] | 48.9 | 47.1 |
Gross Unrealized Gains | [2] | 0.0 | 0.0 |
Gross Unrealized Losses | [2] | 0.0 | 0.0 |
Fair Value | [2] | 48.9 | 47.1 |
Other Cash Deposits [Member] |  |  |  |
Other Temporary Investments |  |  |  |
Cost |  | 13.9 | 9.0 |
Gross Unrealized Gains |  | 0.0 | 0.0 |
Gross Unrealized Losses |  | 0.0 | 0.0 |
Fair Value |  | 13.9 | 9.0 |
Mutual Funds Fixed Income [Member] |  |  |  |
Other Temporary Investments |  |  |  |
Cost | [3] | 165.9 | 152.4 |
Gross Unrealized Gains | [3] | 0.0 | 0.0 |
Gross Unrealized Losses | [3] | (6.2) | (8.3) |
Fair Value | [3] | 159.7 | 144.1 |
Mutual Funds Equity [Member] |  |  |  |
Other Temporary Investments |  |  |  |
Cost |  | 14.8 | 15.1 |
Gross Unrealized Gains |  | 25.9 | 19.4 |
Gross Unrealized Losses |  | 0.0 | 0.0 |
Fair Value |  | 40.7 | 34.5 |
Domestic [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value | [4] | 2,436.6 | 2,131.3 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value | [4] | 2,436.6 | 2,131.3 |
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |
Other than Temporary Impairment Losses, Investments |  | 0.0 | 0.0 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 1,869.5 | 1,483.7 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (0.9) | (6.4) |
Fixed Income Funds [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 1,406.8 | 1,188.7 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 1,406.8 | 1,188.7 |
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |
Other than Temporary Impairment Losses, Investments |  | (41.8) | (28.5) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 33.4 | 12.6 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (9.1) | (22.6) |
Cash and Cash Equivalents [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value | [5] | 16.8 | 21.2 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value | [5] | 16.8 | 21.2 |
Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |
Other than Temporary Impairment Losses, Investments |  | 0.0 | 0.0 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0.0 | 0.0 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0.0 | 0.0 |
US Government Agencies Debt Securities [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 1,273.0 | 1,123.8 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 1,273.0 | 1,123.8 |
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |
Other than Temporary Impairment Losses, Investments |  | (33.2) | (18.8) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 28.6 | 11.8 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (3.9) | (14.9) |
Corporate Debt [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 132.1 | 61.6 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 132.1 | 61.6 |
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |
Other than Temporary Impairment Losses, Investments |  | (8.6) | (9.6) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 4.8 | 0.7 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (5.2) | (7.7) |
State and Local Jurisdiction |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 1.7 | 3.3 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 1.7 | 3.3 |
State and Local Jurisdiction | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |
Other than Temporary Impairment Losses, Investments |  | 0.0 | (0.1) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0.0 | 0.1 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0.0 | 0.0 |
AEP Texas Inc. [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | 5,889.8 | 5,657.8 |
Long-term Debt, Fair Value |  | 5,400.7 | 5,045.8 |
AEP Transmission Co [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | 5,414.4 | 4,782.8 |
Long-term Debt, Fair Value |  | 4,796.9 | 3,940.5 |
Appalachian Power Co [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | 5,588.3 | 5,410.5 |
Long-term Debt, Fair Value |  | 5,390.1 | 5,079.2 |
Indiana Michigan Power Co [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | 3,499.4 | 3,260.8 |
Long-term Debt, Fair Value |  | 3,291.6 | 2,929.0 |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 3,860.2 | 3,341.2 |
Securities Activity Within the Decommissioning and SNF Trusts |  |  |  |
Payments to Acquire Investments |  | 2,845.1 | 2,765.4 | 1,928.2
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 3,860.2 | 3,341.2 |
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Securities Activity Within the Decommissioning and SNF Trusts |  |  |  |
Payments to Acquire Investments |  | 2,845.1 | 2,765.4 | 1,928.2
Realized Investment Gains (Losses) |  | 99.0 | 52.4 | 103.2
Gain (Loss) on Investments |  | 26.6 | 42.6 | 16.5
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Within 1 year |  | 359.6 |  |
After 1 year through 5 years |  | 597.6 |  |
After 5 years through 10 years |  | 180.7 |  |
After 10 years |  | 268.9 |  |
Fair Value Measurements (Textuals) |  |  |  |
Adjusted Cost of Debt Securities |  | 1,400.0 | 1,200.0 |
Adjusted Cost of Domestic Equity Securities |  | 568.0 | 654.0 |
Proceeds from Sale of Other Investments |  | 2,787.5 | 2,713.6 | 1,886.4
Realized Investment Gains (Losses) |  | 99.0 | 52.4 | 103.2
Gain (Loss) on Investments |  | 26.6 | 42.6 | $ 16.5
Other than Temporary Impairment Losses, Investments |  | (41.8) | (28.5) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 1,902.9 | 1,496.3 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (10.0) | (29.0) |
Indiana Michigan Power Co [Member] | Domestic [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value | [4] | 2,436.6 | 2,131.3 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value | [4] | 2,436.6 | 2,131.3 |
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 | 0.0 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 1,869.5 | 1,483.7 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (0.9) | (6.4) |
Indiana Michigan Power Co [Member] | Fixed Income Funds [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 1,406.8 | 1,188.7 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 1,406.8 | 1,188.7 |
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 |  | (41.8) | (28.5) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 33.4 | 12.6 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (9.1) | (22.6) |
Indiana Michigan Power Co [Member] | Cash and Cash Equivalents [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value | [5] | 16.8 | 21.2 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value | [5] | 16.8 | 21.2 |
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 | 0.0 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0.0 | 0.0 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0.0 | 0.0 |
Indiana Michigan Power Co [Member] | US Government Agencies Debt Securities [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 1,273.0 | 1,123.8 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 1,273.0 | 1,123.8 |
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 |  | (33.2) | (18.8) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 28.6 | 11.8 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (3.9) | (14.9) |
Indiana Michigan Power Co [Member] | Corporate Debt [Member] |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 132.1 | 61.6 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 132.1 | 61.6 |
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 |  | (8.6) | (9.6) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 4.8 | 0.7 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | (5.2) | (7.7) |
Indiana Michigan Power Co [Member] | State and Local Jurisdiction |  |  |  |
Nuclear Trust Fund Investments |  |  |  |
Fair Value |  | 1.7 | 3.3 |
Contractual Maturities, Fair Value of Debt Securities |  |  |  |
Fair Value |  | 1.7 | 3.3 |
Indiana Michigan Power Co [Member] | State and Local Jurisdiction | Spent Nuclear Fuel and Decommissioning Trusts [Member] |  |  |  |
Fair Value Measurements (Textuals) |  |  |  |
Other than Temporary Impairment Losses, Investments |  | 0.0 | (0.1) |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax |  | 0.0 | 0.1 |
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax |  | 0.0 | 0.0 |
Ohio Power Co [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | 3,366.8 | 2,970.3 |
Long-term Debt, Fair Value |  | 2,992.1 | 2,516.6 |
Public Service Co Of Oklahoma [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | 2,384.6 | 1,912.8 |
Long-term Debt, Fair Value |  | 2,154.3 | 1,635.8 |
Southwestern Electric Power Co [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Total Long-term Debt Outstanding |  | 3,646.9 | 3,391.6 |
Long-term Debt, Fair Value |  | 3,209.7 | 2,870.9 |
Equity units [Member] |  |  |  |
Book Values and Fair Values of Long - term Debt |  |  |  |
Long-term Debt, Fair Value |  | $ 0.0 | $ 877.0 |
[1] | The fair value amounts include debt related to AEP’s Equity Units and had a fair value of $0 million and $877 million as of December 31, 2023 and 2022, respectively. See “Equity Units” section of Note 14 for additional information.
[2] | Primarily represents amounts held for the repayment of debt.
[3] | Primarily short and intermediate maturities which may be sold and do not contain maturity dates.
[4] | Amounts represent publicly-traded equity securities and equity-based mutual funds.
[5] | Amounts in “Other” column primarily represent accrued interest receivables from financial institutions. Level 1 amounts primarily represent investments in money market funds.

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