Fair Value Long-term Debt, Other Temporary Investments, Nuclear Trusts (Details) - USD ($) $ in Millions |
12 Months Ended |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
$ 26,725.5
|
|
$ 23,346.7
|
|
Long-term Debt, Fair Value |
30,172.0
|
|
24,093.9
|
|
Other Temporary Investments |
|
|
|
|
Cost |
367.1
|
|
355.0
|
|
Gross Unrealized Gains |
21.4
|
|
16.4
|
|
Gross Unrealized Losses |
0.0
|
|
(2.3)
|
|
Fair Value |
388.5
|
|
369.1
|
|
Debt and Equity Securities Within Other Temporary Investments |
|
|
|
|
Proceeds From Investment Sales |
21.2
|
|
0.0
|
$ 0.0
|
Purchases of Investments |
45.0
|
|
3.1
|
14.2
|
Gross Realized Gains on Investment Sales |
0.0
|
|
0.0
|
0.0
|
Gross Realized Losses on Investment Sales |
0.4
|
|
0.0
|
0.0
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
2,975.7
|
|
2,474.9
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
2,975.7
|
|
2,474.9
|
|
Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
1,205.9
|
|
794.7
|
|
Other-Than-Temporary Impairments |
(7.9)
|
|
(9.2)
|
|
Securities Activity Within the Decommissioning and SNF Trusts |
|
|
|
|
Proceeds from Investment Sales |
1,473.0
|
|
2,010.0
|
2,256.3
|
Purchases of Investments |
1,531.0
|
|
2,064.7
|
2,300.5
|
Gross Realized Gains on Investment Sales |
76.5
|
|
47.5
|
200.7
|
Gross Realized Losses on Investment Sales |
24.3
|
|
32.8
|
146.0
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Within 1 year |
371.0
|
|
|
|
After 1 year through 5 years |
386.2
|
|
|
|
After 5 years through 10 years |
217.3
|
|
|
|
After 10 years |
218.0
|
|
|
|
Fair Value Measurements (Textuals) |
|
|
|
|
Adjusted Cost of Debt Securities |
1,100.0
|
|
1,000.0
|
|
Adjusted Cost of Domestic Equity Securities |
623.0
|
|
629.0
|
|
AEP Texas Inc. [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
4,558.4
|
|
3,881.3
|
|
Long-term Debt, Fair Value |
4,981.5
|
|
3,964.6
|
|
AEP Transmission Co [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
3,427.3
|
|
2,823.0
|
|
Long-term Debt, Fair Value |
3,868.0
|
|
2,782.4
|
|
Appalachian Power Co [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
4,363.8
|
|
4,062.6
|
|
Long-term Debt, Fair Value |
5,253.1
|
|
4,473.3
|
|
Indiana Michigan Power Co [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
3,050.2
|
|
3,035.4
|
|
Long-term Debt, Fair Value |
3,453.8
|
|
3,070.2
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
2,975.7
|
|
2,474.9
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
2,975.7
|
|
2,474.9
|
|
Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
1,205.9
|
|
794.7
|
|
Other-Than-Temporary Impairments |
(7.9)
|
|
(9.2)
|
|
Securities Activity Within the Decommissioning and SNF Trusts |
|
|
|
|
Proceeds from Investment Sales |
1,473.0
|
|
2,010.0
|
2,256.3
|
Purchases of Investments |
1,531.0
|
|
2,064.7
|
2,300.5
|
Gross Realized Gains on Investment Sales |
76.5
|
|
47.5
|
200.7
|
Gross Realized Losses on Investment Sales |
24.3
|
|
32.8
|
$ 146.0
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Within 1 year |
371.0
|
|
|
|
After 1 year through 5 years |
386.2
|
|
|
|
After 5 years through 10 years |
217.3
|
|
|
|
After 10 years |
218.0
|
|
|
|
Fair Value Measurements (Textuals) |
|
|
|
|
Adjusted Cost of Debt Securities |
1,100.0
|
|
1,000.0
|
|
Adjusted Cost of Domestic Equity Securities |
623.0
|
|
629.0
|
|
Ohio Power Co [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
2,082.0
|
|
1,716.6
|
|
Long-term Debt, Fair Value |
2,554.3
|
|
1,919.7
|
|
Public Service Co Of Oklahoma [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
1,386.2
|
|
1,287.0
|
|
Long-term Debt, Fair Value |
1,603.3
|
|
1,361.9
|
|
Southwestern Electric Power Co [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Total Long-term Debt Outstanding |
2,655.6
|
|
2,713.4
|
|
Long-term Debt, Fair Value |
2,927.9
|
|
2,670.2
|
|
Cash [Member] |
|
|
|
|
Other Temporary Investments |
|
|
|
|
Cost |
214.7
|
|
230.6
|
|
Gross Unrealized Gains |
0.0
|
|
0.0
|
|
Gross Unrealized Losses |
0.0
|
|
0.0
|
|
Fair Value |
214.7
|
|
230.6
|
|
Fixed Income Funds [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
1,192.5
|
|
1,057.1
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
1,192.5
|
|
1,057.1
|
|
Fixed Income Funds [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
61.5
|
|
28.4
|
|
Other-Than-Temporary Impairments |
(7.9)
|
|
(9.2)
|
|
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
1,192.5
|
|
1,057.1
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
1,192.5
|
|
1,057.1
|
|
Fixed Income Funds [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
61.5
|
|
28.4
|
|
Other-Than-Temporary Impairments |
(7.9)
|
|
(9.2)
|
|
Mutual Funds Fixed Income [Member] |
|
|
|
|
Other Temporary Investments |
|
|
|
|
Cost |
123.2
|
|
106.6
|
|
Gross Unrealized Gains |
0.1
|
|
0.0
|
|
Gross Unrealized Losses |
0.0
|
|
(2.3)
|
|
Fair Value |
123.3
|
|
104.3
|
|
Domestic [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
1,767.9
|
|
1,395.3
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
1,767.9
|
|
1,395.3
|
|
Domestic [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Unrealized Gain on Securities |
1,100.0
|
|
784.0
|
|
Unrealized Loss on Securities |
5.0
|
|
18.0
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
1,144.4
|
|
766.3
|
|
Other-Than-Temporary Impairments |
0.0
|
|
0.0
|
|
Domestic [Member] | Indiana Michigan Power Co [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
1,767.9
|
|
1,395.3
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
1,767.9
|
|
1,395.3
|
|
Domestic [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Unrealized Gain on Securities |
1,100.0
|
|
784.0
|
|
Unrealized Loss on Securities |
5.0
|
|
18.0
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
1,144.4
|
[1] |
766.3
|
|
Other-Than-Temporary Impairments |
0.0
|
[1] |
0.0
|
|
Mutual Funds Equity [Member] |
|
|
|
|
Other Temporary Investments |
|
|
|
|
Cost |
29.2
|
|
17.8
|
|
Gross Unrealized Gains |
21.3
|
|
16.4
|
|
Gross Unrealized Losses |
0.0
|
|
0.0
|
|
Fair Value |
50.5
|
|
34.2
|
|
Cash and Cash Equivalents [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
15.3
|
|
22.5
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
15.3
|
|
22.5
|
|
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 |
15.3
|
|
22.5
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
15.3
|
|
22.5
|
|
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 |
1,112.5
|
|
996.1
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
1,112.5
|
|
996.1
|
|
US Government Agencies Debt Securities [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
55.5
|
|
26.7
|
|
Other-Than-Temporary Impairments |
(6.1)
|
|
(7.1)
|
|
US Government Agencies Debt Securities [Member] | Indiana Michigan Power Co [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
1,112.5
|
|
996.1
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
1,112.5
|
|
996.1
|
|
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 |
55.5
|
|
26.7
|
|
Other-Than-Temporary Impairments |
(6.1)
|
|
(7.1)
|
|
Corporate Debt [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
72.4
|
|
52.4
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
72.4
|
|
52.4
|
|
Corporate Debt [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
5.3
|
|
1.1
|
|
Other-Than-Temporary Impairments |
(1.6)
|
|
(1.9)
|
|
Corporate Debt [Member] | Indiana Michigan Power Co [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
72.4
|
|
52.4
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
72.4
|
|
52.4
|
|
Corporate Debt [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
5.3
|
|
1.1
|
|
Other-Than-Temporary Impairments |
(1.6)
|
|
(1.9)
|
|
State and Local Jurisdiction [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
7.6
|
|
8.6
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
7.6
|
|
8.6
|
|
State and Local Jurisdiction [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
0.7
|
|
0.6
|
|
Other-Than-Temporary Impairments |
(0.2)
|
|
(0.2)
|
|
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Fair Value |
7.6
|
|
8.6
|
|
Contractual Maturities, Fair Value of Debt Securities |
|
|
|
|
Fair Value |
7.6
|
|
8.6
|
|
State and Local Jurisdiction [Member] | Indiana Michigan Power Co [Member] | Spent Nuclear Fuel and Decommissioning Trusts [Member] |
|
|
|
|
Nuclear Trust Fund Investments |
|
|
|
|
Gross Unrealized Gains |
0.7
|
|
0.6
|
|
Other-Than-Temporary Impairments |
(0.2)
|
|
$ (0.2)
|
|
Equity units [Member] |
|
|
|
|
Book Values and Fair Values of Long - term Debt |
|
|
|
|
Long-term Debt, Fair Value |
$ 871.0
|
|
|
|
|
|