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Debt
 3 Months Ended
Mar. 31, 2024
Debt [Line Items]  
Debt DEBT
NOTE 7(a) Short-term Debt - In March 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $200 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):
March 31, 2024Alliant EnergyIPLWPL
Amount outstanding$334$—$—
Weighted average interest rates5.5%—%—%
Available credit facility capacity$666$200$300
Alliant EnergyIPLWPL
Three Months Ended March 31202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$14$—$390$349
Average amount outstanding (based on daily outstanding balances)$487$574$1$—$255$304
Weighted average interest rates5.5%4.8%5.5%—%5.5%4.8%

NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of March 31, 2024) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2025. This term loan credit agreement amends and restates 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 term loan credit 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. In March 2024, WPL issued $300 million of 5.375% debentures due 2034. WPL’s debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds will be allocated or disbursed for the development and acquisition of WPL’s solar EGUs.

Convertible Senior Notes - As of March 31, 2024, the conditions allowing holders of Alliant Energy’s convertible senior notes due 2026 (the Notes) to convert their Notes were not met, and as a result, the Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet. As of March 31, 2024, the net carrying amount of the Notes was $569 million, with unamortized debt issuance costs of $6 million, and the estimated fair value (Level 2) of the Notes was $567 million. As of March 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.
IPL [Member]  
Debt [Line Items]  
Debt DEBT
NOTE 7(a) Short-term Debt - In March 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $200 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):
March 31, 2024Alliant EnergyIPLWPL
Amount outstanding$334$—$—
Weighted average interest rates5.5%—%—%
Available credit facility capacity$666$200$300
Alliant EnergyIPLWPL
Three Months Ended March 31202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$14$—$390$349
Average amount outstanding (based on daily outstanding balances)$487$574$1$—$255$304
Weighted average interest rates5.5%4.8%5.5%—%5.5%4.8%
WPL [Member]  
Debt [Line Items]  
Debt DEBT
NOTE 7(a) Short-term Debt - In March 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $500 million for Alliant Energy at the parent company level, $200 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions):
March 31, 2024Alliant EnergyIPLWPL
Amount outstanding$334$—$—
Weighted average interest rates5.5%—%—%
Available credit facility capacity$666$200$300
Alliant EnergyIPLWPL
Three Months Ended March 31202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$14$—$390$349
Average amount outstanding (based on daily outstanding balances)$487$574$1$—$255$304
Weighted average interest rates5.5%4.8%5.5%—%5.5%4.8%

NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of March 31, 2024) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2025. This term loan credit agreement amends and restates 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 term loan credit 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. In March 2024, WPL issued $300 million of 5.375% debentures due 2034. WPL’s debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds will be allocated or disbursed for the development and acquisition of WPL’s solar EGUs.