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Debt | 12 Months Ended
--- | ---
Dec. 31, 2021
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, 2021, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2026, totaled $1 billion ($450 million for Alliant Energy at the parent company level, $250 million for IPL and $300 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 $500 million, $400 million and $500 million, respectively, within the $1 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, classified as short-term debt was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Amount outstanding | $515 |  | $389 |  | $— |  | $— |  | $236 |  | $257
Weighted average interest rates | 0.2% |  | 0.2% |  | N/A |  | N/A |  | 0.2% |  | 0.1%
Available credit facility capacity | $485 |  | $611 |  | $250 |  | $250 |  | $64 |  | $43
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Maximum amount outstanding (based on daily outstanding balances) | $648 |  | $495 |  | $19 |  | $8 |  | $320 |  | $266
Average amount outstanding (based on daily outstanding balances) | $459 |  | $292 |  | $— |  | $— |  | $172 |  | $117
Weighted average interest rates | 0.2% |  | 0.7% |  | 0.2% |  | 0.5% |  | 0.1% |  | 0.7%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2021 |  | 2020
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.25%, due 2024 | $500 |  |  | $500 |  |  | $— |  |  | $500 |  |  | $500 |  |  | $— |
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 |  |  | — |
6.45%, due 2033 | 100 |  |  | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |
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 (b) | 300 |  |  | 300 |  |  | — |  |  | — |  |  | — |  |  | — |
| 3,675 |  |  | 3,675 |  |  | — |  |  | 3,375 |  |  | 3,375 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
2.25%, due 2022 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
3.05%, due 2027 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3%, due 2029 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
1.95%, due 2031 (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 |
| 2,450 |  |  | — |  |  | 2,450 |  |  | 2,150 |  |  | — |  |  | 2,150 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through March 2022, 1% at December 31, 2021 (with Alliant Energy as guarantor) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Corporate Services 3.45% senior notes, due 2022 (a) | 75 |  |  | — |  |  | — |  |  | 75 |  |  | — |  |  | — |
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a) | 400 |  |  | — |  |  | — |  |  | 400 |  |  | — |  |  | — |
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a) | 200 |  |  | — |  |  | — |  |  | 200 |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes, due 2022 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) | 24 |  |  | — |  |  | — |  |  | 31 |  |  | — |  |  | — |
Other, 1% at December 31, 2021, due 2022 to 2025 | 1 |  |  | — |  |  | — |  |  | 2 |  |  | — |  |  | — |
| 1,300 |  |  | — |  |  | — |  |  | 1,308 |  |  | — |  |  | — |
Subtotal | 7,425 |  |  | 3,675 |  |  | 2,450 |  |  | 6,833 |  |  | 3,375 |  |  | 2,150 |
Current maturities | (633) |  |  | — |  |  | (250) |  |  | (8) |  |  | — |  |  | — |
Unamortized debt issuance costs | (42) |  |  | (23) |  |  | (15) |  |  | (41) |  |  | (22) |  |  | (14) |
Unamortized debt (discount) and premium, net | (15) |  |  | (9) |  |  | (6) |  |  | (15) |  |  | (8) |  |  | (6) |
Long-term debt, net (d) | $6,735 |  |  | $3,643 |  |  | $2,179 |  |  | $6,769 |  |  | $3,345 |  |  | $2,130 |
(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 November 2021, IPL issued $300 million of 3.1% senior debentures due 2051. The net proceeds from the issuance were used by IPL to retire its cumulative preferred stock in 2021 and for general corporate purposes. (c)In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount in excess of the net proceeds was disbursed for the construction and development of WPL’s wind and solar EGUs. (d)There were no significant sinking fund requirements related to the outstanding long-term debt. Five-Year Schedule of Long-term Debt Maturities - At December 31, 2021, long-term debt maturities for 2022 through 2026 were as follows (in millions):
| 2022 |  | 2023 |  | 2024 |  | 2025 |  | 2026
IPL | $— |  | $— |  | $500 |  | $300 |  | $—
WPL | 250 |  | — |  | — |  | — |  | —
Corporate Services | 75 |  | — |  | — |  | — |  | —
AEF | 308 |  | 408 |  | 9 |  | — |  | 200
Alliant Energy | $633 |  | $408 |  | $509 |  | $300 |  | $200
Fair Value of Long-term Debt - Refer to Note 16 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, 2021, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2026, totaled $1 billion ($450 million for Alliant Energy at the parent company level, $250 million for IPL and $300 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 $500 million, $400 million and $500 million, respectively, within the $1 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, classified as short-term debt was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Amount outstanding | $515 |  | $389 |  | $— |  | $— |  | $236 |  | $257
Weighted average interest rates | 0.2% |  | 0.2% |  | N/A |  | N/A |  | 0.2% |  | 0.1%
Available credit facility capacity | $485 |  | $611 |  | $250 |  | $250 |  | $64 |  | $43
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Maximum amount outstanding (based on daily outstanding balances) | $648 |  | $495 |  | $19 |  | $8 |  | $320 |  | $266
Average amount outstanding (based on daily outstanding balances) | $459 |  | $292 |  | $— |  | $— |  | $172 |  | $117
Weighted average interest rates | 0.2% |  | 0.7% |  | 0.2% |  | 0.5% |  | 0.1% |  | 0.7%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2021 |  | 2020
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.25%, due 2024 | $500 |  |  | $500 |  |  | $— |  |  | $500 |  |  | $500 |  |  | $— |
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 |  |  | — |
6.45%, due 2033 | 100 |  |  | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |
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 (b) | 300 |  |  | 300 |  |  | — |  |  | — |  |  | — |  |  | — |
| 3,675 |  |  | 3,675 |  |  | — |  |  | 3,375 |  |  | 3,375 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
2.25%, due 2022 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
3.05%, due 2027 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3%, due 2029 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
1.95%, due 2031 (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 |
| 2,450 |  |  | — |  |  | 2,450 |  |  | 2,150 |  |  | — |  |  | 2,150 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through March 2022, 1% at December 31, 2021 (with Alliant Energy as guarantor) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Corporate Services 3.45% senior notes, due 2022 (a) | 75 |  |  | — |  |  | — |  |  | 75 |  |  | — |  |  | — |
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a) | 400 |  |  | — |  |  | — |  |  | 400 |  |  | — |  |  | — |
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a) | 200 |  |  | — |  |  | — |  |  | 200 |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes, due 2022 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) | 24 |  |  | — |  |  | — |  |  | 31 |  |  | — |  |  | — |
Other, 1% at December 31, 2021, due 2022 to 2025 | 1 |  |  | — |  |  | — |  |  | 2 |  |  | — |  |  | — |
| 1,300 |  |  | — |  |  | — |  |  | 1,308 |  |  | — |  |  | — |
Subtotal | 7,425 |  |  | 3,675 |  |  | 2,450 |  |  | 6,833 |  |  | 3,375 |  |  | 2,150 |
Current maturities | (633) |  |  | — |  |  | (250) |  |  | (8) |  |  | — |  |  | — |
Unamortized debt issuance costs | (42) |  |  | (23) |  |  | (15) |  |  | (41) |  |  | (22) |  |  | (14) |
Unamortized debt (discount) and premium, net | (15) |  |  | (9) |  |  | (6) |  |  | (15) |  |  | (8) |  |  | (6) |
Long-term debt, net (d) | $6,735 |  |  | $3,643 |  |  | $2,179 |  |  | $6,769 |  |  | $3,345 |  |  | $2,130 |
(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 November 2021, IPL issued $300 million of 3.1% senior debentures due 2051. The net proceeds from the issuance were used by IPL to retire its cumulative preferred stock in 2021 and for general corporate purposes. (c)In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount in excess of the net proceeds was disbursed for the construction and development of WPL’s wind and solar EGUs. (d)There were no significant sinking fund requirements related to the outstanding long-term debt. Five-Year Schedule of Long-term Debt Maturities - At December 31, 2021, long-term debt maturities for 2022 through 2026 were as follows (in millions):
| 2022 |  | 2023 |  | 2024 |  | 2025 |  | 2026
IPL | $— |  | $— |  | $500 |  | $300 |  | $—
WPL | 250 |  | — |  | — |  | — |  | —
Corporate Services | 75 |  | — |  | — |  | — |  | —
AEF | 308 |  | 408 |  | 9 |  | — |  | 200
Alliant Energy | $633 |  | $408 |  | $509 |  | $300 |  | $200
Fair Value of Long-term Debt - Refer to Note 16 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, 2021, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2026, totaled $1 billion ($450 million for Alliant Energy at the parent company level, $250 million for IPL and $300 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 $500 million, $400 million and $500 million, respectively, within the $1 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, classified as short-term debt was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Amount outstanding | $515 |  | $389 |  | $— |  | $— |  | $236 |  | $257
Weighted average interest rates | 0.2% |  | 0.2% |  | N/A |  | N/A |  | 0.2% |  | 0.1%
Available credit facility capacity | $485 |  | $611 |  | $250 |  | $250 |  | $64 |  | $43
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Maximum amount outstanding (based on daily outstanding balances) | $648 |  | $495 |  | $19 |  | $8 |  | $320 |  | $266
Average amount outstanding (based on daily outstanding balances) | $459 |  | $292 |  | $— |  | $— |  | $172 |  | $117
Weighted average interest rates | 0.2% |  | 0.7% |  | 0.2% |  | 0.5% |  | 0.1% |  | 0.7%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2021 |  | 2020
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.25%, due 2024 | $500 |  |  | $500 |  |  | $— |  |  | $500 |  |  | $500 |  |  | $— |
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 |  |  | — |
6.45%, due 2033 | 100 |  |  | 100 |  |  | — |  |  | 100 |  |  | 100 |  |  | — |
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 (b) | 300 |  |  | 300 |  |  | — |  |  | — |  |  | — |  |  | — |
| 3,675 |  |  | 3,675 |  |  | — |  |  | 3,375 |  |  | 3,375 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
2.25%, due 2022 | 250 |  |  | — |  |  | 250 |  |  | 250 |  |  | — |  |  | 250 |
3.05%, due 2027 | 300 |  |  | — |  |  | 300 |  |  | 300 |  |  | — |  |  | 300 |
3%, due 2029 | 350 |  |  | — |  |  | 350 |  |  | 350 |  |  | — |  |  | 350 |
1.95%, due 2031 (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 |
| 2,450 |  |  | — |  |  | 2,450 |  |  | 2,150 |  |  | — |  |  | 2,150 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through March 2022, 1% at December 31, 2021 (with Alliant Energy as guarantor) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Corporate Services 3.45% senior notes, due 2022 (a) | 75 |  |  | — |  |  | — |  |  | 75 |  |  | — |  |  | — |
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a) | 400 |  |  | — |  |  | — |  |  | 400 |  |  | — |  |  | — |
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a) | 200 |  |  | — |  |  | — |  |  | 200 |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a) | 300 |  |  | — |  |  | — |  |  | 300 |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes, due 2022 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) | 24 |  |  | — |  |  | — |  |  | 31 |  |  | — |  |  | — |
Other, 1% at December 31, 2021, due 2022 to 2025 | 1 |  |  | — |  |  | — |  |  | 2 |  |  | — |  |  | — |
| 1,300 |  |  | — |  |  | — |  |  | 1,308 |  |  | — |  |  | — |
Subtotal | 7,425 |  |  | 3,675 |  |  | 2,450 |  |  | 6,833 |  |  | 3,375 |  |  | 2,150 |
Current maturities | (633) |  |  | — |  |  | (250) |  |  | (8) |  |  | — |  |  | — |
Unamortized debt issuance costs | (42) |  |  | (23) |  |  | (15) |  |  | (41) |  |  | (22) |  |  | (14) |
Unamortized debt (discount) and premium, net | (15) |  |  | (9) |  |  | (6) |  |  | (15) |  |  | (8) |  |  | (6) |
Long-term debt, net (d) | $6,735 |  |  | $3,643 |  |  | $2,179 |  |  | $6,769 |  |  | $3,345 |  |  | $2,130 |
(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 November 2021, IPL issued $300 million of 3.1% senior debentures due 2051. The net proceeds from the issuance were used by IPL to retire its cumulative preferred stock in 2021 and for general corporate purposes. (c)In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount in excess of the net proceeds was disbursed for the construction and development of WPL’s wind and solar EGUs. (d)There were no significant sinking fund requirements related to the outstanding long-term debt. Five-Year Schedule of Long-term Debt Maturities - At December 31, 2021, long-term debt maturities for 2022 through 2026 were as follows (in millions):
| 2022 |  | 2023 |  | 2024 |  | 2025 |  | 2026
IPL | $— |  | $— |  | $500 |  | $300 |  | $—
WPL | 250 |  | — |  | — |  | — |  | —
Corporate Services | 75 |  | — |  | — |  | — |  | —
AEF | 308 |  | 408 |  | 9 |  | — |  | 200
Alliant Energy | $633 |  | $408 |  | $509 |  | $300 |  | $200
Fair Value of Long-term Debt - Refer to Note 16 for information on the fair value of long-term debt outstanding.

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