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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2020
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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Tax-related | $890 |  |  | $818 |  |  | $843 |  |  | $777 |  |  | $47 |  |  | $41 |
Pension and OPEB costs | 580 |  |  | 524 |  |  | 291 |  |  | 263 |  |  | 289 |  |  | 261 |
AROs | 119 |  |  | 112 |  |  | 81 |  |  | 76 |  |  | 38 |  |  | 36 |
Assets retired early | 113 |  |  | 134 |  |  | 77 |  |  | 88 |  |  | 36 |  |  | 46 |
IPL’s DAEC PPA amendment | 110 |  |  | 108 |  |  | 110 |  |  | 108 |  |  | — |  |  | — |
WPL’s Western Wisconsin gas distribution expansion investments | 55 |  |  | — |  |  | — |  |  | — |  |  | 55 |  |  | — |
Derivatives | 26 |  |  | 39 |  |  | 13 |  |  | 18 |  |  | 13 |  |  | 21 |
Other | 117 |  |  | 110 |  |  | 68 |  |  | 70 |  |  | 49 |  |  | 40 |
| $2,010 |  |  | $1,845 |  |  | $1,483 |  |  | $1,400 |  |  | $527 |  |  | $445 |
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, 2020 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | $23 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 21 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 33 |  | Return of remaining net book value through 2028 |  | IUB and FERC
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 13 |  | Return of and return on remaining net book value through 2022 |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 23 |  | 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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Tax-related | $732 |  | $836 |  | $331 |  | $351 |  | $401 |  | $485
Cost of removal obligations | 367 |  | 388 |  | 238 |  | 257 |  | 129 |  | 131
Electric transmission cost recovery | 68 |  | 88 |  | 39 |  | 51 |  | 29 |  | 37
WPL’s West Riverside liquidated damages | 38 |  | — |  | — |  | — |  | 38 |  | —
Derivatives | 28 |  | 20 |  | 25 |  | 17 |  | 3 |  | 3
Other | 73 |  | 92 |  | 43 |  | 39 |  | 30 |  | 53
| $1,306 |  | $1,424 |  | $676 |  | $715 |  | $630 |  | $709
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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Tax-related | $890 |  |  | $818 |  |  | $843 |  |  | $777 |  |  | $47 |  |  | $41 |
Pension and OPEB costs | 580 |  |  | 524 |  |  | 291 |  |  | 263 |  |  | 289 |  |  | 261 |
AROs | 119 |  |  | 112 |  |  | 81 |  |  | 76 |  |  | 38 |  |  | 36 |
Assets retired early | 113 |  |  | 134 |  |  | 77 |  |  | 88 |  |  | 36 |  |  | 46 |
IPL’s DAEC PPA amendment | 110 |  |  | 108 |  |  | 110 |  |  | 108 |  |  | — |  |  | — |
WPL’s Western Wisconsin gas distribution expansion investments | 55 |  |  | — |  |  | — |  |  | — |  |  | 55 |  |  | — |
Derivatives | 26 |  |  | 39 |  |  | 13 |  |  | 18 |  |  | 13 |  |  | 21 |
Other | 117 |  |  | 110 |  |  | 68 |  |  | 70 |  |  | 49 |  |  | 40 |
| $2,010 |  |  | $1,845 |  |  | $1,483 |  |  | $1,400 |  |  | $527 |  |  | $445 |
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, 2020 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | $23 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 21 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 33 |  | Return of remaining net book value through 2028 |  | IUB and FERC
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 13 |  | Return of and return on remaining net book value through 2022 |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 23 |  | 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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Tax-related | $732 |  | $836 |  | $331 |  | $351 |  | $401 |  | $485
Cost of removal obligations | 367 |  | 388 |  | 238 |  | 257 |  | 129 |  | 131
Electric transmission cost recovery | 68 |  | 88 |  | 39 |  | 51 |  | 29 |  | 37
WPL’s West Riverside liquidated damages | 38 |  | — |  | — |  | — |  | 38 |  | —
Derivatives | 28 |  | 20 |  | 25 |  | 17 |  | 3 |  | 3
Other | 73 |  | 92 |  | 43 |  | 39 |  | 30 |  | 53
| $1,306 |  | $1,424 |  | $676 |  | $715 |  | $630 |  | $709
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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Tax-related | $890 |  |  | $818 |  |  | $843 |  |  | $777 |  |  | $47 |  |  | $41 |
Pension and OPEB costs | 580 |  |  | 524 |  |  | 291 |  |  | 263 |  |  | 289 |  |  | 261 |
AROs | 119 |  |  | 112 |  |  | 81 |  |  | 76 |  |  | 38 |  |  | 36 |
Assets retired early | 113 |  |  | 134 |  |  | 77 |  |  | 88 |  |  | 36 |  |  | 46 |
IPL’s DAEC PPA amendment | 110 |  |  | 108 |  |  | 110 |  |  | 108 |  |  | — |  |  | — |
WPL’s Western Wisconsin gas distribution expansion investments | 55 |  |  | — |  |  | — |  |  | — |  |  | 55 |  |  | — |
Derivatives | 26 |  |  | 39 |  |  | 13 |  |  | 18 |  |  | 13 |  |  | 21 |
Other | 117 |  |  | 110 |  |  | 68 |  |  | 70 |  |  | 49 |  |  | 40 |
| $2,010 |  |  | $1,845 |  |  | $1,483 |  |  | $1,400 |  |  | $527 |  |  | $445 |
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, 2020 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  | $23 |  | Return of and return on remaining net book value through 2027 |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 21 |  | Return of and return on remaining net book value through 2029 |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 33 |  | Return of remaining net book value through 2028 |  | IUB and FERC
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 13 |  | Return of and return on remaining net book value through 2022 |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 23 |  | 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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Tax-related | $732 |  | $836 |  | $331 |  | $351 |  | $401 |  | $485
Cost of removal obligations | 367 |  | 388 |  | 238 |  | 257 |  | 129 |  | 131
Electric transmission cost recovery | 68 |  | 88 |  | 39 |  | 51 |  | 29 |  | 37
WPL’s West Riverside liquidated damages | 38 |  | — |  | — |  | — |  | 38 |  | —
Derivatives | 28 |  | 20 |  | 25 |  | 17 |  | 3 |  | 3
Other | 73 |  | 92 |  | 43 |  | 39 |  | 30 |  | 53
| $1,306 |  | $1,424 |  | $676 |  | $715 |  | $630 |  | $709

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