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Debt (Tables) | 9 Months Ended
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Sep. 30, 2025
Short-term Debt [Line Items] |
Schedule of Other Short-term Borrowings | Information regarding commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
September 30, 2025 | Alliant Energy |  | IPL |  | WPL
Amount outstanding | $192 |  | $— |  | $192
Weighted average interest rates | 4.3% |  | N/A |  | 4.3%
Available credit facility capacity | $1,108 |  | $350 |  | $208
| Alliant Energy |  | IPL |  | WPL
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Maximum amount outstanding (based on daily outstanding balances) | $372 |  | $330 |  | $78 |  | $— |  | $297 |  | $—
Average amount outstanding (based on daily outstanding balances) | $263 |  | $197 |  | $9 |  | $— |  | $177 |  | $—
Weighted average interest rates | 4.5% |  | 5.4% |  | 4.6% |  | N/A |  | 4.5% |  | N/A
Nine Months Ended September 30 |  |  |  |  |  |  |  |  |  |  |
Maximum amount outstanding (based on daily outstanding balances) | $741 |  | $632 |  | $141 |  | $19 |  | $297 |  | $390
Average amount outstanding (based on daily outstanding balances) | $417 |  | $320 |  | $32 |  | $1 |  | $187 |  | $87
Weighted average interest rates | 4.6% |  | 5.5% |  | 4.6% |  | 5.5% |  | 4.5% |  | 5.5%
IPL [Member] |
Short-term Debt [Line Items] |
Schedule of Other Short-term Borrowings | Information regarding commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
September 30, 2025 | Alliant Energy |  | IPL |  | WPL
Amount outstanding | $192 |  | $— |  | $192
Weighted average interest rates | 4.3% |  | N/A |  | 4.3%
Available credit facility capacity | $1,108 |  | $350 |  | $208
| Alliant Energy |  | IPL |  | WPL
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Maximum amount outstanding (based on daily outstanding balances) | $372 |  | $330 |  | $78 |  | $— |  | $297 |  | $—
Average amount outstanding (based on daily outstanding balances) | $263 |  | $197 |  | $9 |  | $— |  | $177 |  | $—
Weighted average interest rates | 4.5% |  | 5.4% |  | 4.6% |  | N/A |  | 4.5% |  | N/A
Nine Months Ended September 30 |  |  |  |  |  |  |  |  |  |  |
Maximum amount outstanding (based on daily outstanding balances) | $741 |  | $632 |  | $141 |  | $19 |  | $297 |  | $390
Average amount outstanding (based on daily outstanding balances) | $417 |  | $320 |  | $32 |  | $1 |  | $187 |  | $87
Weighted average interest rates | 4.6% |  | 5.5% |  | 4.6% |  | 5.5% |  | 4.5% |  | 5.5%
WPL [Member] |
Short-term Debt [Line Items] |
Schedule of Other Short-term Borrowings | Information regarding commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
September 30, 2025 | Alliant Energy |  | IPL |  | WPL
Amount outstanding | $192 |  | $— |  | $192
Weighted average interest rates | 4.3% |  | N/A |  | 4.3%
Available credit facility capacity | $1,108 |  | $350 |  | $208
| Alliant Energy |  | IPL |  | WPL
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Maximum amount outstanding (based on daily outstanding balances) | $372 |  | $330 |  | $78 |  | $— |  | $297 |  | $—
Average amount outstanding (based on daily outstanding balances) | $263 |  | $197 |  | $9 |  | $— |  | $177 |  | $—
Weighted average interest rates | 4.5% |  | 5.4% |  | 4.6% |  | N/A |  | 4.5% |  | N/A
Nine Months Ended September 30 |  |  |  |  |  |  |  |  |  |  |
Maximum amount outstanding (based on daily outstanding balances) | $741 |  | $632 |  | $141 |  | $19 |  | $297 |  | $390
Average amount outstanding (based on daily outstanding balances) | $417 |  | $320 |  | $32 |  | $1 |  | $187 |  | $87
Weighted average interest rates | 4.6% |  | 5.5% |  | 4.6% |  | 5.5% |  | 4.5% |  | 5.5%

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- Definition Tabular disclosure of short-term debt arrangements (having initial terms of repayment within one year or the normal operating cycle, if longer) including: (1) description of the short-term debt arrangement; (2) identification of the lender or type of lender; (3) repayment terms; (4) weighted average interest rate; (5) carrying amount of funds borrowed under the specified short-term debt arrangement as of the balance sheet date; (6) description of the refinancing of a short-term obligation when that obligation is excluded from current liabilities in the balance sheet; and (7) amount of a short-term obligation that has been excluded from current liabilities in the balance sheet because of a refinancing of the obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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