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Debt | 12 Months Ended
--- | ---
Dec. 31, 2024
Debt Instrument [Line Items] |
Debt | DEBT(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2024, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2029, totaled $1.3 billion ($600 million for Alliant Energy at the parent company level, $300 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. 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%
(b) 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. Convertible Senior Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the Notes prior to the maturity date. Holders may convert their Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances: •during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period; •during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or •upon the occurrence of specified corporate events. On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their Notes at any time, regardless of the foregoing circumstances. Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the Notes being converted. The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of Notes (equivalent to an initial conversion price of approximately $64.32 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its Notes in connection with such a corporate event. If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the Notes may require Alliant Energy to repurchase for cash all or any portion of its Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. As of December 31, 2024, the conditions allowing holders of the Notes to convert their Notes were not met. As of December 31, 2024 and 2023, the Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt” and “Long-term debt, net,” respectively. As of December 31, 2024 and 2023, the net carrying amount of the Notes was $571 million and $568 million, with unamortized debt issuance costs of $4 million and $7 million, and the estimated fair value (Level 2) of the Notes was $591 million and $572 million. As of December 31, 2024, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes. Five-Year Schedule of Long-term Debt Maturities - 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
Fair Value of Long-term Debt - Refer to Note 1 5 for information on the fair value of long-term debt outstanding.
IPL [Member] |
Debt Instrument [Line Items] |
Debt | DEBT(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2024, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2029, totaled $1.3 billion ($600 million for Alliant Energy at the parent company level, $300 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. 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%
(b) 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. Convertible Senior Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the Notes prior to the maturity date. Holders may convert their Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances: •during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period; •during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or •upon the occurrence of specified corporate events. On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their Notes at any time, regardless of the foregoing circumstances. Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the Notes being converted. The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of Notes (equivalent to an initial conversion price of approximately $64.32 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its Notes in connection with such a corporate event. If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the Notes may require Alliant Energy to repurchase for cash all or any portion of its Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. As of December 31, 2024, the conditions allowing holders of the Notes to convert their Notes were not met. As of December 31, 2024 and 2023, the Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt” and “Long-term debt, net,” respectively. As of December 31, 2024 and 2023, the net carrying amount of the Notes was $571 million and $568 million, with unamortized debt issuance costs of $4 million and $7 million, and the estimated fair value (Level 2) of the Notes was $591 million and $572 million. As of December 31, 2024, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes. Five-Year Schedule of Long-term Debt Maturities - 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
Fair Value of Long-term Debt - Refer to Note 1 5 for information on the fair value of long-term debt outstanding.
WPL [Member] |
Debt Instrument [Line Items] |
Debt | DEBT(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2024, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2029, totaled $1.3 billion ($600 million for Alliant Energy at the parent company level, $300 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. 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%
(b) 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. Convertible Senior Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the Notes prior to the maturity date. Holders may convert their Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances: •during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period; •during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or •upon the occurrence of specified corporate events. On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their Notes at any time, regardless of the foregoing circumstances. Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the Notes being converted. The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of Notes (equivalent to an initial conversion price of approximately $64.32 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its Notes in connection with such a corporate event. If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the Notes may require Alliant Energy to repurchase for cash all or any portion of its Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. As of December 31, 2024, the conditions allowing holders of the Notes to convert their Notes were not met. As of December 31, 2024 and 2023, the Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt” and “Long-term debt, net,” respectively. As of December 31, 2024 and 2023, the net carrying amount of the Notes was $571 million and $568 million, with unamortized debt issuance costs of $4 million and $7 million, and the estimated fair value (Level 2) of the Notes was $591 million and $572 million. As of December 31, 2024, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes. Five-Year Schedule of Long-term Debt Maturities - 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
Fair Value of Long-term Debt - Refer to Note 1 5 for information on the fair value of long-term debt outstanding.

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