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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2021
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
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Tax-related | $934 |  |  | $890 |  |  | $884 |  |  | $843 |  |  | $50 |  |  | $47 |
Pension and OPEB costs | 462 |  |  | 580 |  |  | 228 |  |  | 291 |  |  | 234 |  |  | 289 |
AROs | 128 |  |  | 119 |  |  | 89 |  |  | 81 |  |  | 39 |  |  | 38 |
Assets retired early | 92 |  |  | 113 |  |  | 66 |  |  | 77 |  |  | 26 |  |  | 36 |
IPL’s DAEC PPA amendment | 90 |  |  | 110 |  |  | 90 |  |  | 110 |  |  | — |  |  | — |
WPL’s Western Wisconsin gas distribution expansion investments | 52 |  |  | 55 |  |  | — |  |  | — |  |  | 52 |  |  | 55 |
Commodity cost recovery | 42 |  |  | 4 |  |  | 2 |  |  | 1 |  |  | 40 |  |  | 3 |
Derivatives | 8 |  |  | 26 |  |  | 4 |  |  | 13 |  |  | 4 |  |  | 13 |
Other | 132 |  |  | 113 |  |  | 80 |  |  | 67 |  |  | 52 |  |  | 46 |
| $1,940 |  |  | $2,010 |  |  | $1,443 |  |  | $1,483 |  |  | $497 |  |  | $527 |
Schedule of 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, 2021 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | $19 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 18 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 29 |  | Return of remaining net book value through 2028 |  | IUB and FERC
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 6 |  | Return of and return on remaining net book value through 2022 |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 20 |  | Return of and return on remaining net book value through 2028 |  | PSCW and FERC
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Tax-related | $585 |  | $732 |  | $312 |  | $331 |  | $273 |  | $401
Cost of removal obligations | 384 |  | 367 |  | 252 |  | 238 |  | 132 |  | 129
Derivatives | 166 |  | 28 |  | 77 |  | 25 |  | 89 |  | 3
Electric transmission cost recovery | 51 |  | 68 |  | 27 |  | 39 |  | 24 |  | 29
WPL’s West Riverside liquidated damages | 36 |  | 38 |  | — |  | — |  | 36 |  | 38
Other | 49 |  | 73 |  | 23 |  | 43 |  | 26 |  | 30
| $1,271 |  | $1,306 |  | $691 |  | $676 |  | $580 |  | $630
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
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Tax-related | $934 |  |  | $890 |  |  | $884 |  |  | $843 |  |  | $50 |  |  | $47 |
Pension and OPEB costs | 462 |  |  | 580 |  |  | 228 |  |  | 291 |  |  | 234 |  |  | 289 |
AROs | 128 |  |  | 119 |  |  | 89 |  |  | 81 |  |  | 39 |  |  | 38 |
Assets retired early | 92 |  |  | 113 |  |  | 66 |  |  | 77 |  |  | 26 |  |  | 36 |
IPL’s DAEC PPA amendment | 90 |  |  | 110 |  |  | 90 |  |  | 110 |  |  | — |  |  | — |
WPL’s Western Wisconsin gas distribution expansion investments | 52 |  |  | 55 |  |  | — |  |  | — |  |  | 52 |  |  | 55 |
Commodity cost recovery | 42 |  |  | 4 |  |  | 2 |  |  | 1 |  |  | 40 |  |  | 3 |
Derivatives | 8 |  |  | 26 |  |  | 4 |  |  | 13 |  |  | 4 |  |  | 13 |
Other | 132 |  |  | 113 |  |  | 80 |  |  | 67 |  |  | 52 |  |  | 46 |
| $1,940 |  |  | $2,010 |  |  | $1,443 |  |  | $1,483 |  |  | $497 |  |  | $527 |
Schedule of 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, 2021 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | $19 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 18 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 29 |  | Return of remaining net book value through 2028 |  | IUB and FERC
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 6 |  | Return of and return on remaining net book value through 2022 |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 20 |  | Return of and return on remaining net book value through 2028 |  | PSCW and FERC
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Tax-related | $585 |  | $732 |  | $312 |  | $331 |  | $273 |  | $401
Cost of removal obligations | 384 |  | 367 |  | 252 |  | 238 |  | 132 |  | 129
Derivatives | 166 |  | 28 |  | 77 |  | 25 |  | 89 |  | 3
Electric transmission cost recovery | 51 |  | 68 |  | 27 |  | 39 |  | 24 |  | 29
WPL’s West Riverside liquidated damages | 36 |  | 38 |  | — |  | — |  | 36 |  | 38
Other | 49 |  | 73 |  | 23 |  | 43 |  | 26 |  | 30
| $1,271 |  | $1,306 |  | $691 |  | $676 |  | $580 |  | $630
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
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Tax-related | $934 |  |  | $890 |  |  | $884 |  |  | $843 |  |  | $50 |  |  | $47 |
Pension and OPEB costs | 462 |  |  | 580 |  |  | 228 |  |  | 291 |  |  | 234 |  |  | 289 |
AROs | 128 |  |  | 119 |  |  | 89 |  |  | 81 |  |  | 39 |  |  | 38 |
Assets retired early | 92 |  |  | 113 |  |  | 66 |  |  | 77 |  |  | 26 |  |  | 36 |
IPL’s DAEC PPA amendment | 90 |  |  | 110 |  |  | 90 |  |  | 110 |  |  | — |  |  | — |
WPL’s Western Wisconsin gas distribution expansion investments | 52 |  |  | 55 |  |  | — |  |  | — |  |  | 52 |  |  | 55 |
Commodity cost recovery | 42 |  |  | 4 |  |  | 2 |  |  | 1 |  |  | 40 |  |  | 3 |
Derivatives | 8 |  |  | 26 |  |  | 4 |  |  | 13 |  |  | 4 |  |  | 13 |
Other | 132 |  |  | 113 |  |  | 80 |  |  | 67 |  |  | 52 |  |  | 46 |
| $1,940 |  |  | $2,010 |  |  | $1,443 |  |  | $1,483 |  |  | $497 |  |  | $527 |
Schedule of 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, 2021 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | $19 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 18 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 29 |  | Return of remaining net book value through 2028 |  | IUB and FERC
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 6 |  | Return of and return on remaining net book value through 2022 |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 20 |  | Return of and return on remaining net book value through 2028 |  | PSCW and FERC
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Tax-related | $585 |  | $732 |  | $312 |  | $331 |  | $273 |  | $401
Cost of removal obligations | 384 |  | 367 |  | 252 |  | 238 |  | 132 |  | 129
Derivatives | 166 |  | 28 |  | 77 |  | 25 |  | 89 |  | 3
Electric transmission cost recovery | 51 |  | 68 |  | 27 |  | 39 |  | 24 |  | 29
WPL’s West Riverside liquidated damages | 36 |  | 38 |  | — |  | — |  | 36 |  | 38
Other | 49 |  | 73 |  | 23 |  | 43 |  | 26 |  | 30
| $1,271 |  | $1,306 |  | $691 |  | $676 |  | $580 |  | $630

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