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Debt (Tables) | 12 Months Ended
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Dec. 31, 2024
Debt Instrument [Line Items] |
Schedule of Other Short-term Borrowings | Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Amount outstanding | $558 |  | $475 |  | $50 |  | $— |  | $183 |  | $318
Weighted average interest rates | 4.5% |  | 5.5% |  | 4.6% |  | N/A |  | 4.5% |  | 5.4%
Available credit facility capacity | $742 |  | $525 |  | $250 |  | $150 |  | $217 |  | $82
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Maximum amount outstanding (based on daily outstanding balances) | $632 |  | $793 |  | $80 |  | $70 |  | $390 |  | $349
Average amount outstanding (based on daily outstanding balances) | $327 |  | $386 |  | $1 |  | $2 |  | $70 |  | $157
Weighted average interest rates | 5.3% |  | 5.2% |  | 5.1% |  | 5.3% |  | 5.4% |  | 5.1%
Schedule of Long-term Debt | Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2024 |  | 2023
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.4%, due 2025 | $250 |  |  | $250 |  |  | $— |  |  | $250 |  |  | $250 |  |  | $— |
5.5%, due 2025 | 50 |  |  | 50 |  |  | — |  |  | 50 |  |  | 50 |  |  | — |
4.1%, due 2028 | 500 |  |  | 500 |  |  | — |  |  | 500 |  |  | 500 |  |  | — |
3.6%, due 2029 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
2.3%, due 2030 | 400 |  |  | 400 |  |  | — |  |  | 400 |  |  | 400 |  |  | — |
5.7%, due 2033 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
6.45%, due 2033 | 100 |  |  | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |
4.95%, due 2034 (b) | 350 |  |  | 350 |  |  | — |  |  | — |  |  | — |  |  | — |
6.3%, due 2034 | 125 |  |  | 125 |  |  | — |  |  | 125 |  |  | 125 |  |  | — |
6.25%, due 2039 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
4.7%, due 2043 | 250 |  |  | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |
3.7%, due 2046 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
3.5%, due 2049 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
3.1%, due 2051 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
5.45%, due 2054 (b) | 300 |  |  | 300 |  |  | — |  |  | — |  |  | — |  |  | — |
3.25% (Retired in 2024) | — |  |  | — |  |  | — |  |  | 500 |  |  | 500 |  |  | — |
| 4,125 |  |  | 4,125 |  |  | — |  |  | 3,975 |  |  | 3,975 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.05%, due 2027 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3%, due 2029 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
1.95%, due 2031 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3.95%, due 2032 | 600 |  |  | — |  |  | 600 |  |  | 600 |  |  | — |  |  | 600 |
4.95% due 2033 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
5.375%, due 2034 (c) | 300 |  |  | — |  |  | 300 |  |  | — |  |  | — |  |  | — |
6.25%, due 2034 | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |  |  | 100 |
6.375%, due 2037 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
7.6%, due 2038 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
4.1%, due 2044 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
3.65%, due 2050 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
| 3,400 |  |  | — |  |  | 3,400 |  |  | 3,100 |  |  | — |  |  | 3,100 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (with Alliant Energy as guarantor) (d) | 300 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a) | 200 |  |  | — |  |  | — |  |  | 200 |  |  | — |  |  | — |
Alliant Energy 3.875% convertible senior notes, due 2026 (e) | 575 |  |  | — |  |  | — |  |  | 575 |  |  | — |  |  | — |
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)(f) | 375 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) | 350 |  |  | — |  |  | — |  |  | 350 |  |  | — |  |  | — |
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d) | — |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024) | — |  |  | — |  |  | — |  |  | 9 |  |  | — |  |  | — |
| 2,400 |  |  | — |  |  | — |  |  | 2,034 |  |  | — |  |  | — |
Subtotal | 9,925 |  |  | 4,125 |  |  | 3,400 |  |  | 9,109 |  |  | 3,975 |  |  | 3,100 |
Current maturities | (1,171) |  |  | (300) |  |  | — |  |  | (809) |  |  | (500) |  |  | — |
Unamortized debt issuance costs | (55) |  |  | (25) |  |  | (20) |  |  | (54) |  |  | (21) |  |  | (19) |
Unamortized debt (discount) and premium, net | (22) |  |  | (10) |  |  | (10) |  |  | (21) |  |  | (9) |  |  | (11) |
Long-term debt, net (g) | $8,677 |  |  | $3,790 |  |  | $3,370 |  |  | $8,225 |  |  | $3,445 |  |  | $3,070 |
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b)In September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes. (c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs. (d)In March 2024, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 1 4 for information on AEF’s related interest rate swap. (e)Refer to “Convertible Senior Notes” below for additional information. (f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. (g)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt | At December 31, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
| 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029
IPL | $300 |  | $— |  | $— |  | $500 |  | $300
WPL | — |  | — |  | 300 |  | — |  | 350
AEF | 300 |  | 200 |  | 375 |  | 300 |  | 300
Alliant Energy parent company | — |  | 575 |  | — |  | — |  | —
Alliant Energy | $600 |  | $775 |  | $675 |  | $800 |  | $950
IPL [Member] |
Debt Instrument [Line Items] |
Schedule of Other Short-term Borrowings | Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Amount outstanding | $558 |  | $475 |  | $50 |  | $— |  | $183 |  | $318
Weighted average interest rates | 4.5% |  | 5.5% |  | 4.6% |  | N/A |  | 4.5% |  | 5.4%
Available credit facility capacity | $742 |  | $525 |  | $250 |  | $150 |  | $217 |  | $82
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Maximum amount outstanding (based on daily outstanding balances) | $632 |  | $793 |  | $80 |  | $70 |  | $390 |  | $349
Average amount outstanding (based on daily outstanding balances) | $327 |  | $386 |  | $1 |  | $2 |  | $70 |  | $157
Weighted average interest rates | 5.3% |  | 5.2% |  | 5.1% |  | 5.3% |  | 5.4% |  | 5.1%
Schedule of Long-term Debt | Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2024 |  | 2023
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.4%, due 2025 | $250 |  |  | $250 |  |  | $— |  |  | $250 |  |  | $250 |  |  | $— |
5.5%, due 2025 | 50 |  |  | 50 |  |  | — |  |  | 50 |  |  | 50 |  |  | — |
4.1%, due 2028 | 500 |  |  | 500 |  |  | — |  |  | 500 |  |  | 500 |  |  | — |
3.6%, due 2029 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
2.3%, due 2030 | 400 |  |  | 400 |  |  | — |  |  | 400 |  |  | 400 |  |  | — |
5.7%, due 2033 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
6.45%, due 2033 | 100 |  |  | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |
4.95%, due 2034 (b) | 350 |  |  | 350 |  |  | — |  |  | — |  |  | — |  |  | — |
6.3%, due 2034 | 125 |  |  | 125 |  |  | — |  |  | 125 |  |  | 125 |  |  | — |
6.25%, due 2039 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
4.7%, due 2043 | 250 |  |  | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |
3.7%, due 2046 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
3.5%, due 2049 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
3.1%, due 2051 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
5.45%, due 2054 (b) | 300 |  |  | 300 |  |  | — |  |  | — |  |  | — |  |  | — |
3.25% (Retired in 2024) | — |  |  | — |  |  | — |  |  | 500 |  |  | 500 |  |  | — |
| 4,125 |  |  | 4,125 |  |  | — |  |  | 3,975 |  |  | 3,975 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.05%, due 2027 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3%, due 2029 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
1.95%, due 2031 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3.95%, due 2032 | 600 |  |  | — |  |  | 600 |  |  | 600 |  |  | — |  |  | 600 |
4.95% due 2033 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
5.375%, due 2034 (c) | 300 |  |  | — |  |  | 300 |  |  | — |  |  | — |  |  | — |
6.25%, due 2034 | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |  |  | 100 |
6.375%, due 2037 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
7.6%, due 2038 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
4.1%, due 2044 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
3.65%, due 2050 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
| 3,400 |  |  | — |  |  | 3,400 |  |  | 3,100 |  |  | — |  |  | 3,100 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (with Alliant Energy as guarantor) (d) | 300 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a) | 200 |  |  | — |  |  | — |  |  | 200 |  |  | — |  |  | — |
Alliant Energy 3.875% convertible senior notes, due 2026 (e) | 575 |  |  | — |  |  | — |  |  | 575 |  |  | — |  |  | — |
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)(f) | 375 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) | 350 |  |  | — |  |  | — |  |  | 350 |  |  | — |  |  | — |
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d) | — |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024) | — |  |  | — |  |  | — |  |  | 9 |  |  | — |  |  | — |
| 2,400 |  |  | — |  |  | — |  |  | 2,034 |  |  | — |  |  | — |
Subtotal | 9,925 |  |  | 4,125 |  |  | 3,400 |  |  | 9,109 |  |  | 3,975 |  |  | 3,100 |
Current maturities | (1,171) |  |  | (300) |  |  | — |  |  | (809) |  |  | (500) |  |  | — |
Unamortized debt issuance costs | (55) |  |  | (25) |  |  | (20) |  |  | (54) |  |  | (21) |  |  | (19) |
Unamortized debt (discount) and premium, net | (22) |  |  | (10) |  |  | (10) |  |  | (21) |  |  | (9) |  |  | (11) |
Long-term debt, net (g) | $8,677 |  |  | $3,790 |  |  | $3,370 |  |  | $8,225 |  |  | $3,445 |  |  | $3,070 |
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b)In September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes. (c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs. (d)In March 2024, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 1 4 for information on AEF’s related interest rate swap. (e)Refer to “Convertible Senior Notes” below for additional information. (f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. (g)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt | At December 31, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
| 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029
IPL | $300 |  | $— |  | $— |  | $500 |  | $300
WPL | — |  | — |  | 300 |  | — |  | 350
AEF | 300 |  | 200 |  | 375 |  | 300 |  | 300
Alliant Energy parent company | — |  | 575 |  | — |  | — |  | —
Alliant Energy | $600 |  | $775 |  | $675 |  | $800 |  | $950
WPL [Member] |
Debt Instrument [Line Items] |
Schedule of Other Short-term Borrowings | Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Amount outstanding | $558 |  | $475 |  | $50 |  | $— |  | $183 |  | $318
Weighted average interest rates | 4.5% |  | 5.5% |  | 4.6% |  | N/A |  | 4.5% |  | 5.4%
Available credit facility capacity | $742 |  | $525 |  | $250 |  | $150 |  | $217 |  | $82
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Maximum amount outstanding (based on daily outstanding balances) | $632 |  | $793 |  | $80 |  | $70 |  | $390 |  | $349
Average amount outstanding (based on daily outstanding balances) | $327 |  | $386 |  | $1 |  | $2 |  | $70 |  | $157
Weighted average interest rates | 5.3% |  | 5.2% |  | 5.1% |  | 5.3% |  | 5.4% |  | 5.1%
Schedule of Long-term Debt | Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2024 |  | 2023
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.4%, due 2025 | $250 |  |  | $250 |  |  | $— |  |  | $250 |  |  | $250 |  |  | $— |
5.5%, due 2025 | 50 |  |  | 50 |  |  | — |  |  | 50 |  |  | 50 |  |  | — |
4.1%, due 2028 | 500 |  |  | 500 |  |  | — |  |  | 500 |  |  | 500 |  |  | — |
3.6%, due 2029 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
2.3%, due 2030 | 400 |  |  | 400 |  |  | — |  |  | 400 |  |  | 400 |  |  | — |
5.7%, due 2033 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
6.45%, due 2033 | 100 |  |  | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |
4.95%, due 2034 (b) | 350 |  |  | 350 |  |  | — |  |  | — |  |  | — |  |  | — |
6.3%, due 2034 | 125 |  |  | 125 |  |  | — |  |  | 125 |  |  | 125 |  |  | — |
6.25%, due 2039 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
4.7%, due 2043 | 250 |  |  | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |
3.7%, due 2046 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
3.5%, due 2049 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
3.1%, due 2051 | 300 |  |  | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |
5.45%, due 2054 (b) | 300 |  |  | 300 |  |  | — |  |  | — |  |  | — |  |  | — |
3.25% (Retired in 2024) | — |  |  | — |  |  | — |  |  | 500 |  |  | 500 |  |  | — |
| 4,125 |  |  | 4,125 |  |  | — |  |  | 3,975 |  |  | 3,975 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.05%, due 2027 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3%, due 2029 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
1.95%, due 2031 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3.95%, due 2032 | 600 |  |  | — |  |  | 600 |  |  | 600 |  |  | — |  |  | 600 |
4.95% due 2033 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
5.375%, due 2034 (c) | 300 |  |  | — |  |  | 300 |  |  | — |  |  | — |  |  | — |
6.25%, due 2034 | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |  |  | 100 |
6.375%, due 2037 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
7.6%, due 2038 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
4.1%, due 2044 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
3.65%, due 2050 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
| 3,400 |  |  | — |  |  | 3,400 |  |  | 3,100 |  |  | — |  |  | 3,100 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (with Alliant Energy as guarantor) (d) | 300 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a) | 200 |  |  | — |  |  | — |  |  | 200 |  |  | — |  |  | — |
Alliant Energy 3.875% convertible senior notes, due 2026 (e) | 575 |  |  | — |  |  | — |  |  | 575 |  |  | — |  |  | — |
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)(f) | 375 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) | 350 |  |  | — |  |  | — |  |  | 350 |  |  | — |  |  | — |
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d) | — |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024) | — |  |  | — |  |  | — |  |  | 9 |  |  | — |  |  | — |
| 2,400 |  |  | — |  |  | — |  |  | 2,034 |  |  | — |  |  | — |
Subtotal | 9,925 |  |  | 4,125 |  |  | 3,400 |  |  | 9,109 |  |  | 3,975 |  |  | 3,100 |
Current maturities | (1,171) |  |  | (300) |  |  | — |  |  | (809) |  |  | (500) |  |  | — |
Unamortized debt issuance costs | (55) |  |  | (25) |  |  | (20) |  |  | (54) |  |  | (21) |  |  | (19) |
Unamortized debt (discount) and premium, net | (22) |  |  | (10) |  |  | (10) |  |  | (21) |  |  | (9) |  |  | (11) |
Long-term debt, net (g) | $8,677 |  |  | $3,790 |  |  | $3,370 |  |  | $8,225 |  |  | $3,445 |  |  | $3,070 |
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b)In September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes. (c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs. (d)In March 2024, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 1 4 for information on AEF’s related interest rate swap. (e)Refer to “Convertible Senior Notes” below for additional information. (f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. (g)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt | At December 31, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
| 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029
IPL | $300 |  | $— |  | $— |  | $500 |  | $300
WPL | — |  | — |  | 300 |  | — |  | 350
AEF | 300 |  | 200 |  | 375 |  | 300 |  | 300
Alliant Energy parent company | — |  | 575 |  | — |  | — |  | —
Alliant Energy | $600 |  | $775 |  | $675 |  | $800 |  | $950

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