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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2023
Regulatory Assets [Line Items] |
Schedule of Regulatory Assets | At December 31, regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Tax-related | $934 |  |  | $929 |  |  | $831 |  |  | $848 |  |  | $103 |  |  | $81 |
Pension and OPEB costs | 347 |  |  | 392 |  |  | 171 |  |  | 197 |  |  | 176 |  |  | 195 |
Assets retired early | 273 |  |  | 70 |  |  | 259 |  |  | 53 |  |  | 14 |  |  | 17 |
AROs | 194 |  |  | 151 |  |  | 160 |  |  | 110 |  |  | 34 |  |  | 41 |
Commodity cost recovery | 120 |  |  | 160 |  |  | 12 |  |  | 1 |  |  | 108 |  |  | 159 |
Derivatives | 102 |  |  | 84 |  |  | 34 |  |  | 48 |  |  | 68 |  |  | 36 |
WPL’s Western Wisconsin gas distribution expansion investments | 44 |  |  | 48 |  |  | — |  |  | — |  |  | 44 |  |  | 48 |
IPL’s DAEC PPA amendment | 42 |  |  | 66 |  |  | 42 |  |  | 66 |  |  | — |  |  | — |
Other | 205 |  |  | 146 |  |  | 68 |  |  | 63 |  |  | 137 |  |  | 83 |
| $2,261 |  |  | $2,046 |  |  | $1,577 |  |  | $1,386 |  |  | $684 |  |  | $660 |
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):
Entity |  | Asset |  | Retirement Date |  | Regulatory Asset Balance as of Dec. 31, 2023 |  | Recovery |  | Regulatory Approval
IPL |  | Lansing |  | 2023 |  | $216 |  | Return of and return on remaining net book value through 2037 |  | FERC and pending with the IUB (a)
IPL |  | Analog electric meters |  | 2019 |  | 20 |  | Return of remaining net book value through 2028 |  | IUB and FERC
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | 12 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 11 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 14 |  | Return of and return on remaining net book value through 2028 |  | PSCW and FERC
(a)IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037.
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Tax-related | $566 |  | $579 |  | $299 |  | $303 |  | $267 |  | $276
Cost of removal obligations | 366 |  | 398 |  | 242 |  | 259 |  | 124 |  | 139
Derivatives | 65 |  | 210 |  | 34 |  | 115 |  | 31 |  | 95
Commodity cost recovery | 48 |  | 40 |  | 13 |  | 38 |  | 35 |  | 2
WPL’s West Riverside liquidated damages | 1 |  | 32 |  | — |  | — |  | 1 |  | 32
Other | 84 |  | 65 |  | 56 |  | 39 |  | 28 |  | 26
| $1,130 |  | $1,324 |  | $644 |  | $754 |  | $486 |  | $570
IPL [Member] |
Regulatory Assets [Line Items] |
Schedule of Regulatory Assets | At December 31, regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Tax-related | $934 |  |  | $929 |  |  | $831 |  |  | $848 |  |  | $103 |  |  | $81 |
Pension and OPEB costs | 347 |  |  | 392 |  |  | 171 |  |  | 197 |  |  | 176 |  |  | 195 |
Assets retired early | 273 |  |  | 70 |  |  | 259 |  |  | 53 |  |  | 14 |  |  | 17 |
AROs | 194 |  |  | 151 |  |  | 160 |  |  | 110 |  |  | 34 |  |  | 41 |
Commodity cost recovery | 120 |  |  | 160 |  |  | 12 |  |  | 1 |  |  | 108 |  |  | 159 |
Derivatives | 102 |  |  | 84 |  |  | 34 |  |  | 48 |  |  | 68 |  |  | 36 |
WPL’s Western Wisconsin gas distribution expansion investments | 44 |  |  | 48 |  |  | — |  |  | — |  |  | 44 |  |  | 48 |
IPL’s DAEC PPA amendment | 42 |  |  | 66 |  |  | 42 |  |  | 66 |  |  | — |  |  | — |
Other | 205 |  |  | 146 |  |  | 68 |  |  | 63 |  |  | 137 |  |  | 83 |
| $2,261 |  |  | $2,046 |  |  | $1,577 |  |  | $1,386 |  |  | $684 |  |  | $660 |
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):
Entity |  | Asset |  | Retirement Date |  | Regulatory Asset Balance as of Dec. 31, 2023 |  | Recovery |  | Regulatory Approval
IPL |  | Lansing |  | 2023 |  | $216 |  | Return of and return on remaining net book value through 2037 |  | FERC and pending with the IUB (a)
IPL |  | Analog electric meters |  | 2019 |  | 20 |  | Return of remaining net book value through 2028 |  | IUB and FERC
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | 12 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 11 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 14 |  | Return of and return on remaining net book value through 2028 |  | PSCW and FERC
(a)IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037.
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Tax-related | $566 |  | $579 |  | $299 |  | $303 |  | $267 |  | $276
Cost of removal obligations | 366 |  | 398 |  | 242 |  | 259 |  | 124 |  | 139
Derivatives | 65 |  | 210 |  | 34 |  | 115 |  | 31 |  | 95
Commodity cost recovery | 48 |  | 40 |  | 13 |  | 38 |  | 35 |  | 2
WPL’s West Riverside liquidated damages | 1 |  | 32 |  | — |  | — |  | 1 |  | 32
Other | 84 |  | 65 |  | 56 |  | 39 |  | 28 |  | 26
| $1,130 |  | $1,324 |  | $644 |  | $754 |  | $486 |  | $570
WPL [Member] |
Regulatory Assets [Line Items] |
Schedule of Regulatory Assets | At December 31, regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Tax-related | $934 |  |  | $929 |  |  | $831 |  |  | $848 |  |  | $103 |  |  | $81 |
Pension and OPEB costs | 347 |  |  | 392 |  |  | 171 |  |  | 197 |  |  | 176 |  |  | 195 |
Assets retired early | 273 |  |  | 70 |  |  | 259 |  |  | 53 |  |  | 14 |  |  | 17 |
AROs | 194 |  |  | 151 |  |  | 160 |  |  | 110 |  |  | 34 |  |  | 41 |
Commodity cost recovery | 120 |  |  | 160 |  |  | 12 |  |  | 1 |  |  | 108 |  |  | 159 |
Derivatives | 102 |  |  | 84 |  |  | 34 |  |  | 48 |  |  | 68 |  |  | 36 |
WPL’s Western Wisconsin gas distribution expansion investments | 44 |  |  | 48 |  |  | — |  |  | — |  |  | 44 |  |  | 48 |
IPL’s DAEC PPA amendment | 42 |  |  | 66 |  |  | 42 |  |  | 66 |  |  | — |  |  | — |
Other | 205 |  |  | 146 |  |  | 68 |  |  | 63 |  |  | 137 |  |  | 83 |
| $2,261 |  |  | $2,046 |  |  | $1,577 |  |  | $1,386 |  |  | $684 |  |  | $660 |
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):
Entity |  | Asset |  | Retirement Date |  | Regulatory Asset Balance as of Dec. 31, 2023 |  | Recovery |  | Regulatory Approval
IPL |  | Lansing |  | 2023 |  | $216 |  | Return of and return on remaining net book value through 2037 |  | FERC and pending with the IUB (a)
IPL |  | Analog electric meters |  | 2019 |  | 20 |  | Return of remaining net book value through 2028 |  | IUB and FERC
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | 12 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 11 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 14 |  | Return of and return on remaining net book value through 2028 |  | PSCW and FERC
(a)IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037.
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Tax-related | $566 |  | $579 |  | $299 |  | $303 |  | $267 |  | $276
Cost of removal obligations | 366 |  | 398 |  | 242 |  | 259 |  | 124 |  | 139
Derivatives | 65 |  | 210 |  | 34 |  | 115 |  | 31 |  | 95
Commodity cost recovery | 48 |  | 40 |  | 13 |  | 38 |  | 35 |  | 2
WPL’s West Riverside liquidated damages | 1 |  | 32 |  | — |  | — |  | 1 |  | 32
Other | 84 |  | 65 |  | 56 |  | 39 |  | 28 |  | 26
| $1,130 |  | $1,324 |  | $644 |  | $754 |  | $486 |  | $570

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