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Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding $ 31,072.5 $ 26,725.5  
Long-term Debt, Fair Value [1] 37,457.0 30,172.0  
Other Temporary Investments      
Cost 214.9 367.1  
Gross Unrealized Gains 31.5 21.4  
Gross Unrealized Losses 0.0 0.0  
Fair Value 246.4 388.5  
Debt and Equity Securities Within Other Temporary Investments      
Proceeds From Investment Sales 50.9 21.2 $ 0.0
Purchases of Investments 41.6 45.0 3.1
Gross Realized Gains on Investment Sales 3.8 0.0 0.0
Gross Realized Losses on Investment Sales 0.2 0.4 0.0
Nuclear Trust Fund Investments      
Fair Value 3,306.7 2,975.7  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 3,306.7 2,975.7  
Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 1,509.8 1,205.9  
Other-Than-Temporary Impairments (9.2) (7.9)  
Securities Activity Within the Decommissioning and SNF Trusts      
Proceeds from Investment Sales 1,593.4 1,473.0 2,010.0
Purchases of Investments 1,637.2 1,531.0 2,064.7
Gross Realized Gains on Investment Sales 26.4 76.5 47.5
Gross Realized Losses on Investment Sales 26.1 24.3 32.8
Contractual Maturities, Fair Value of Debt Securities      
Within 1 year 294.8    
After 1 year through 5 years 371.3    
After 5 years through 10 years 214.4    
After 10 years 345.7    
Fair Value Measurements (Textuals)      
Adjusted Cost of Debt Securities 1,100.0 1,100.0  
Adjusted Cost of Domestic Equity Securities 654.0 623.0  
AEP Texas Inc. [Member]      
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding 4,820.4 4,558.4  
Long-term Debt, Fair Value 5,682.6 4,981.5  
AEP Transmission Co [Member]      
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding 3,948.5 3,427.3  
Long-term Debt, Fair Value 4,984.3 3,868.0  
Appalachian Power Co [Member]      
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding 4,834.1 4,363.8  
Long-term Debt, Fair Value 6,391.8 5,253.1  
Indiana Michigan Power Co [Member]      
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding 3,029.9 3,050.2  
Long-term Debt, Fair Value 3,775.3 3,453.8  
Nuclear Trust Fund Investments      
Fair Value 3,306.7 2,975.7  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 3,306.7 2,975.7  
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 1,509.8 1,205.9  
Other-Than-Temporary Impairments (9.2) (7.9)  
Securities Activity Within the Decommissioning and SNF Trusts      
Proceeds from Investment Sales 1,593.4 1,473.0 2,010.0
Purchases of Investments 1,637.2 1,531.0 2,064.7
Gross Realized Gains on Investment Sales 26.4 76.5 47.5
Gross Realized Losses on Investment Sales 26.1 24.3 $ 32.8
Contractual Maturities, Fair Value of Debt Securities      
Within 1 year 294.8    
After 1 year through 5 years 371.3    
After 5 years through 10 years 214.4    
After 10 years 345.7    
Fair Value Measurements (Textuals)      
Adjusted Cost of Debt Securities 1,100.0 1,100.0  
Adjusted Cost of Domestic Equity Securities 654.0 623.0  
Ohio Power Co [Member]      
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding 2,430.2 2,082.0  
Long-term Debt, Fair Value 3,154.9 2,554.3  
Public Service Co Of Oklahoma [Member]      
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding 1,373.8 1,386.2  
Long-term Debt, Fair Value 1,732.1 1,603.3  
Southwestern Electric Power Co [Member]      
Book Values and Fair Values of Long - term Debt      
Total Long-term Debt Outstanding 2,636.4 2,655.6  
Long-term Debt, Fair Value 3,210.1 2,927.9  
Cash [Member]      
Other Temporary Investments      
Cost [2] 68.3 214.7  
Gross Unrealized Gains [2] 0.0 0.0  
Gross Unrealized Losses [2] 0.0 0.0  
Fair Value [2],[3] 68.3 214.7  
Fixed Income Funds [Member]      
Nuclear Trust Fund Investments      
Fair Value 1,226.2 1,192.5  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 1,226.2 1,192.5  
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 109.0 61.5  
Other-Than-Temporary Impairments (9.2) (7.9)  
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member]      
Nuclear Trust Fund Investments      
Fair Value 1,226.2 1,192.5  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 1,226.2 1,192.5  
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 109.0 61.5  
Other-Than-Temporary Impairments (9.2) (7.9)  
Mutual Funds Fixed Income [Member]      
Other Temporary Investments      
Cost [4] 120.7 123.2  
Gross Unrealized Gains [4] 2.8 0.1  
Gross Unrealized Losses [4] 0.0 0.0  
Fair Value [4] 123.5 123.3  
Mutual Funds Equity [Member]      
Other Temporary Investments      
Cost 25.9 29.2  
Gross Unrealized Gains 28.7 21.3  
Gross Unrealized Losses 0.0 0.0  
Fair Value 54.6 50.5  
Domestic [Member]      
Nuclear Trust Fund Investments      
Fair Value [5] 2,054.7 1,767.9  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value [5] 2,054.7 1,767.9  
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Unrealized Gain on Securities 1,400.0 1,100.0  
Unrealized Loss on Securities 9.0 5.0  
Nuclear Trust Fund Investments      
Gross Unrealized Gains [6] 1,400.8 1,144.4  
Other-Than-Temporary Impairments 0.0 0.0  
Domestic [Member] | Indiana Michigan Power Co [Member]      
Nuclear Trust Fund Investments      
Fair Value [5] 2,054.7 1,767.9  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value [5] 2,054.7 1,767.9  
Domestic [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Unrealized Gain on Securities 1,400.0 1,100.0  
Unrealized Loss on Securities 9.0 5.0  
Nuclear Trust Fund Investments      
Gross Unrealized Gains [6] 1,400.8 1,144.4  
Other-Than-Temporary Impairments 0.0 0.0  
Cash and Cash Equivalents [Member]      
Nuclear Trust Fund Investments      
Fair Value [7] 25.8 15.3  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value [7] 25.8 15.3  
Cash and Cash Equivalents [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 0.0 0.0  
Other-Than-Temporary Impairments 0.0 0.0  
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [Member]      
Nuclear Trust Fund Investments      
Fair Value [7] 25.8 15.3  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value [7] 25.8 15.3  
Cash and Cash Equivalents [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 0.0 0.0  
Other-Than-Temporary Impairments 0.0 0.0  
US Government Agencies Debt Securities [Member]      
Nuclear Trust Fund Investments      
Fair Value 1,025.6 1,112.5  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 1,025.6 1,112.5  
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 98.5 55.5  
Other-Than-Temporary Impairments (7.1) (6.1)  
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member]      
Nuclear Trust Fund Investments      
Fair Value 1,025.6 1,112.5  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 1,025.6 1,112.5  
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 98.5 55.5  
Other-Than-Temporary Impairments (7.1) (6.1)  
Corporate Debt [Member]      
Nuclear Trust Fund Investments      
Fair Value 86.3 72.4  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 86.3 72.4  
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 9.6 5.3  
Other-Than-Temporary Impairments (1.7) (1.6)  
Corporate Debt [Member] | Indiana Michigan Power Co [Member]      
Nuclear Trust Fund Investments      
Fair Value 86.3 72.4  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 86.3 72.4  
Corporate Debt [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 9.6 5.3  
Other-Than-Temporary Impairments (1.7) (1.6)  
State and Local Jurisdiction      
Nuclear Trust Fund Investments      
Fair Value 114.3 7.6  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 114.3 7.6  
State and Local Jurisdiction | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 0.9 0.7  
Other-Than-Temporary Impairments (0.4) (0.2)  
State and Local Jurisdiction | Indiana Michigan Power Co [Member]      
Nuclear Trust Fund Investments      
Fair Value 114.3 7.6  
Contractual Maturities, Fair Value of Debt Securities      
Fair Value 114.3 7.6  
State and Local Jurisdiction | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member]      
Nuclear Trust Fund Investments      
Gross Unrealized Gains 0.9 0.7  
Other-Than-Temporary Impairments (0.4) (0.2)  
Equity units [Member]      
Book Values and Fair Values of Long - term Debt      
Long-term Debt, Fair Value $ 1,700.0 $ 871.0 [1]  
[1] The fair value amounts include debt related to AEP’s Equity Units and had a fair value of $1.7 billion and $871 million as of December 31, 2020 and 2019, respectively. See “Equity Units” section of Note 14 for additional information.
[2] Primarily represents amounts held for the repayment of debt.
[3] 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.
[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] Amount reported as Gross Unrealized Gains includes unrealized gains of $1.4 billion and $1.1 billion and unrealized losses of $9 million and $5 million as of December 31, 2020 and 2019, respectively.
[7] Amounts in “Other” column primarily represent accrued interest receivables from financial institutions.  Level 1 amounts primarily represent investments in money market funds.