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Regulatory Matters (Tables)
 12 Months Ended
Dec. 31, 2024
Regulatory Assets [Line Items]  
Schedule of Regulatory Assets At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 
Assets Retired Early Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generation Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.
Schedule of Regulatory Liabilities At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
IPL [Member]  
Regulatory Assets [Line Items]  
Schedule of Regulatory Assets At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 
Assets Retired Early Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generation Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.
Schedule of Regulatory Liabilities At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
WPL [Member]  
Regulatory Assets [Line Items]  
Schedule of Regulatory Assets At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 
Assets Retired Early Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generation Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.
Schedule of Regulatory Liabilities At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486