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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2019
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
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Tax-related |  | $817.6 |  |  |  | $820.6 |  |  |  | $776.8 |  |  |  | $783.1 |  |  |  | $40.8 |  |  |  | $37.5 |
Pension and OPEB costs | 524.0 |  |  | 542.3 |  |  | 262.5 |  |  | 274.0 |  |  | 261.5 |  |  | 268.3 |
Assets retired early | 134.0 |  |  | 111.6 |  |  | 87.9 |  |  | 55.4 |  |  | 46.1 |  |  | 56.2 |
AROs | 111.8 |  |  | 110.8 |  |  | 76.2 |  |  | 76.3 |  |  | 35.6 |  |  | 34.5 |
IPL’s DAEC PPA amendment | 108.2 |  |  | — |  |  | 108.2 |  |  | — |  |  | — |  |  | — |
Derivatives | 39.5 |  |  | 28.0 |  |  | 18.3 |  |  | 15.1 |  |  | 21.2 |  |  | 12.9 |
Emission allowances | 21.1 |  |  | 23.6 |  |  | 21.1 |  |  | 23.6 |  |  | — |  |  | — |
Other | 88.5 |  |  | 100.4 |  |  | 48.3 |  |  | 51.5 |  |  | 40.2 |  |  | 48.9 |
|  | $1,844.7 |  |  |  | $1,737.3 |  |  |  | $1,399.3 |  |  |  | $1,279.0 |  |  |  | $445.4 |  |  |  | $458.3 |
Electric Generating Units 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:
Entity |  | Asset |  | Retirement Date |  | Regulatory Asset Balance as of Dec. 31, 2019 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  |  | $28.5 |  |  | Return of and return on remaining net book value over 10 years (return on effective with new rates expected to be implemented by the end of the first quarter of 2020) |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 23.6 |  |  | Return of and return on remaining net book value over 10 years |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 35.8 |  |  | Return of remaining net book value over 10 years (effective with new rates expected to be implemented by the end of the first quarter of 2020) |  | IUB
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 20.2 |  |  | Return of and return on remaining net book value over 10 years |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 25.9 |  |  | Return of and return on remaining net book value over 10 years |  | PSCW and FERC
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Tax-related |  | $835.6 |  |  |  | $890.6 |  |  |  | $350.9 |  |  |  | $390.1 |  |  |  | $484.7 |  |  |  | $500.5 |
Cost of removal obligations | 387.7 |  |  | 401.2 |  |  | 257.0 |  |  | 273.3 |  |  | 130.7 |  |  | 127.9 |
Electric transmission cost recovery | 88.6 |  |  | 104.0 |  |  | 51.3 |  |  | 47.7 |  |  | 37.3 |  |  | 56.3 |
Commodity cost recovery | 24.2 |  |  | 16.8 |  |  | 8.8 |  |  | 11.9 |  |  | 15.4 |  |  | 4.9 |
WPL’s earnings sharing mechanism | 21.9 |  |  | 25.4 |  |  | — |  |  | — |  |  | 21.9 |  |  | 25.4 |
Derivatives | 19.9 |  |  | 18.5 |  |  | 17.4 |  |  | 10.2 |  |  | 2.5 |  |  | 8.3 |
Other | 45.7 |  |  | 36.7 |  |  | 29.3 |  |  | 21.7 |  |  | 16.4 |  |  | 15.0 |
|  | $1,423.6 |  |  |  | $1,493.2 |  |  |  | $714.7 |  |  |  | $754.9 |  |  |  | $708.9 |  |  |  | $738.3 |
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
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Tax-related |  | $817.6 |  |  |  | $820.6 |  |  |  | $776.8 |  |  |  | $783.1 |  |  |  | $40.8 |  |  |  | $37.5 |
Pension and OPEB costs | 524.0 |  |  | 542.3 |  |  | 262.5 |  |  | 274.0 |  |  | 261.5 |  |  | 268.3 |
Assets retired early | 134.0 |  |  | 111.6 |  |  | 87.9 |  |  | 55.4 |  |  | 46.1 |  |  | 56.2 |
AROs | 111.8 |  |  | 110.8 |  |  | 76.2 |  |  | 76.3 |  |  | 35.6 |  |  | 34.5 |
IPL’s DAEC PPA amendment | 108.2 |  |  | — |  |  | 108.2 |  |  | — |  |  | — |  |  | — |
Derivatives | 39.5 |  |  | 28.0 |  |  | 18.3 |  |  | 15.1 |  |  | 21.2 |  |  | 12.9 |
Emission allowances | 21.1 |  |  | 23.6 |  |  | 21.1 |  |  | 23.6 |  |  | — |  |  | — |
Other | 88.5 |  |  | 100.4 |  |  | 48.3 |  |  | 51.5 |  |  | 40.2 |  |  | 48.9 |
|  | $1,844.7 |  |  |  | $1,737.3 |  |  |  | $1,399.3 |  |  |  | $1,279.0 |  |  |  | $445.4 |  |  |  | $458.3 |
Electric Generating Units 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:
Entity |  | Asset |  | Retirement Date |  | Regulatory Asset Balance as of Dec. 31, 2019 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  |  | $28.5 |  |  | Return of and return on remaining net book value over 10 years (return on effective with new rates expected to be implemented by the end of the first quarter of 2020) |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 23.6 |  |  | Return of and return on remaining net book value over 10 years |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 35.8 |  |  | Return of remaining net book value over 10 years (effective with new rates expected to be implemented by the end of the first quarter of 2020) |  | IUB
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 20.2 |  |  | Return of and return on remaining net book value over 10 years |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 25.9 |  |  | Return of and return on remaining net book value over 10 years |  | PSCW and FERC
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Tax-related |  | $835.6 |  |  |  | $890.6 |  |  |  | $350.9 |  |  |  | $390.1 |  |  |  | $484.7 |  |  |  | $500.5 |
Cost of removal obligations | 387.7 |  |  | 401.2 |  |  | 257.0 |  |  | 273.3 |  |  | 130.7 |  |  | 127.9 |
Electric transmission cost recovery | 88.6 |  |  | 104.0 |  |  | 51.3 |  |  | 47.7 |  |  | 37.3 |  |  | 56.3 |
Commodity cost recovery | 24.2 |  |  | 16.8 |  |  | 8.8 |  |  | 11.9 |  |  | 15.4 |  |  | 4.9 |
WPL’s earnings sharing mechanism | 21.9 |  |  | 25.4 |  |  | — |  |  | — |  |  | 21.9 |  |  | 25.4 |
Derivatives | 19.9 |  |  | 18.5 |  |  | 17.4 |  |  | 10.2 |  |  | 2.5 |  |  | 8.3 |
Other | 45.7 |  |  | 36.7 |  |  | 29.3 |  |  | 21.7 |  |  | 16.4 |  |  | 15.0 |
|  | $1,423.6 |  |  |  | $1,493.2 |  |  |  | $714.7 |  |  |  | $754.9 |  |  |  | $708.9 |  |  |  | $738.3 |
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
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Tax-related |  | $817.6 |  |  |  | $820.6 |  |  |  | $776.8 |  |  |  | $783.1 |  |  |  | $40.8 |  |  |  | $37.5 |
Pension and OPEB costs | 524.0 |  |  | 542.3 |  |  | 262.5 |  |  | 274.0 |  |  | 261.5 |  |  | 268.3 |
Assets retired early | 134.0 |  |  | 111.6 |  |  | 87.9 |  |  | 55.4 |  |  | 46.1 |  |  | 56.2 |
AROs | 111.8 |  |  | 110.8 |  |  | 76.2 |  |  | 76.3 |  |  | 35.6 |  |  | 34.5 |
IPL’s DAEC PPA amendment | 108.2 |  |  | — |  |  | 108.2 |  |  | — |  |  | — |  |  | — |
Derivatives | 39.5 |  |  | 28.0 |  |  | 18.3 |  |  | 15.1 |  |  | 21.2 |  |  | 12.9 |
Emission allowances | 21.1 |  |  | 23.6 |  |  | 21.1 |  |  | 23.6 |  |  | — |  |  | — |
Other | 88.5 |  |  | 100.4 |  |  | 48.3 |  |  | 51.5 |  |  | 40.2 |  |  | 48.9 |
|  | $1,844.7 |  |  |  | $1,737.3 |  |  |  | $1,399.3 |  |  |  | $1,279.0 |  |  |  | $445.4 |  |  |  | $458.3 |
Electric Generating Units 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:
Entity |  | Asset |  | Retirement Date |  | Regulatory Asset Balance as of Dec. 31, 2019 |  | Recovery |  | Regulatory Approval
IPL |  | Sutherland Units 1 and 3 |  | 2017 |  |  | $28.5 |  |  | Return of and return on remaining net book value over 10 years (return on effective with new rates expected to be implemented by the end of the first quarter of 2020) |  | IUB and FERC
IPL |  | M.L. Kapp Unit 2 |  | 2018 |  | 23.6 |  |  | Return of and return on remaining net book value over 10 years |  | IUB and FERC
IPL |  | Analog electric meters |  | 2019 |  | 35.8 |  |  | Return of remaining net book value over 10 years (effective with new rates expected to be implemented by the end of the first quarter of 2020) |  | IUB
WPL |  | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 |  | 2015 |  | 20.2 |  |  | Return of and return on remaining net book value over 10 years |  | PSCW and FERC
WPL |  | Edgewater Unit 4 |  | 2018 |  | 25.9 |  |  | Return of and return on remaining net book value over 10 years |  | PSCW and FERC
Schedule of Regulatory Liabilities | At December 31, regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Tax-related |  | $835.6 |  |  |  | $890.6 |  |  |  | $350.9 |  |  |  | $390.1 |  |  |  | $484.7 |  |  |  | $500.5 |
Cost of removal obligations | 387.7 |  |  | 401.2 |  |  | 257.0 |  |  | 273.3 |  |  | 130.7 |  |  | 127.9 |
Electric transmission cost recovery | 88.6 |  |  | 104.0 |  |  | 51.3 |  |  | 47.7 |  |  | 37.3 |  |  | 56.3 |
Commodity cost recovery | 24.2 |  |  | 16.8 |  |  | 8.8 |  |  | 11.9 |  |  | 15.4 |  |  | 4.9 |
WPL’s earnings sharing mechanism | 21.9 |  |  | 25.4 |  |  | — |  |  | — |  |  | 21.9 |  |  | 25.4 |
Derivatives | 19.9 |  |  | 18.5 |  |  | 17.4 |  |  | 10.2 |  |  | 2.5 |  |  | 8.3 |
Other | 45.7 |  |  | 36.7 |  |  | 29.3 |  |  | 21.7 |  |  | 16.4 |  |  | 15.0 |
|  | $1,423.6 |  |  |  | $1,493.2 |  |  |  | $714.7 |  |  |  | $754.9 |  |  |  | $708.9 |  |  |  | $738.3 |

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