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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2019
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations (AROs) | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Balance, January 1 |  | $177.5 |  |  |  | $184.5 |  |  |  | $118.3 |  |  |  | $134.1 |  |  |  | $59.2 |  |  |  | $50.4 |
Revisions in estimated cash flows | (5.5 | ) |  | (10.1 | ) |  | (6.7 | ) |  | (10.1 | ) |  | 1.2 |  |  | — |
Liabilities settled | (8.8 | ) |  | (10.4 | ) |  | (8.4 | ) |  | (9.7 | ) |  | (0.4 | ) |  | (0.7 | )
Liabilities incurred (a) | 26.2 |  |  | 7.3 |  |  | 26.2 |  |  | — |  |  | — |  |  | 7.3 |
Accretion expense | 6.9 |  |  | 6.2 |  |  | 4.5 |  |  | 4.0 |  |  | 2.4 |  |  | 2.2 |
Balance, December 31 |  | $196.3 |  |  |  | $177.5 |  |  |  | $133.9 |  |  |  | $118.3 |  |  |  | $62.4 |  |  |  | $59.2 |
(a) | In 2019, Alliant Energy and IPL recognized additional AROs related to IPL’s newly constructed Upland Prairie and English Farms wind sites. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
IPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations (AROs) | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Balance, January 1 |  | $177.5 |  |  |  | $184.5 |  |  |  | $118.3 |  |  |  | $134.1 |  |  |  | $59.2 |  |  |  | $50.4 |
Revisions in estimated cash flows | (5.5 | ) |  | (10.1 | ) |  | (6.7 | ) |  | (10.1 | ) |  | 1.2 |  |  | — |
Liabilities settled | (8.8 | ) |  | (10.4 | ) |  | (8.4 | ) |  | (9.7 | ) |  | (0.4 | ) |  | (0.7 | )
Liabilities incurred (a) | 26.2 |  |  | 7.3 |  |  | 26.2 |  |  | — |  |  | — |  |  | 7.3 |
Accretion expense | 6.9 |  |  | 6.2 |  |  | 4.5 |  |  | 4.0 |  |  | 2.4 |  |  | 2.2 |
Balance, December 31 |  | $196.3 |  |  |  | $177.5 |  |  |  | $133.9 |  |  |  | $118.3 |  |  |  | $62.4 |  |  |  | $59.2 |
(a) | In 2019, Alliant Energy and IPL recognized additional AROs related to IPL’s newly constructed Upland Prairie and English Farms wind sites. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
WPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations (AROs) | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Balance, January 1 |  | $177.5 |  |  |  | $184.5 |  |  |  | $118.3 |  |  |  | $134.1 |  |  |  | $59.2 |  |  |  | $50.4 |
Revisions in estimated cash flows | (5.5 | ) |  | (10.1 | ) |  | (6.7 | ) |  | (10.1 | ) |  | 1.2 |  |  | — |
Liabilities settled | (8.8 | ) |  | (10.4 | ) |  | (8.4 | ) |  | (9.7 | ) |  | (0.4 | ) |  | (0.7 | )
Liabilities incurred (a) | 26.2 |  |  | 7.3 |  |  | 26.2 |  |  | — |  |  | — |  |  | 7.3 |
Accretion expense | 6.9 |  |  | 6.2 |  |  | 4.5 |  |  | 4.0 |  |  | 2.4 |  |  | 2.2 |
Balance, December 31 |  | $196.3 |  |  |  | $177.5 |  |  |  | $133.9 |  |  |  | $118.3 |  |  |  | $62.4 |  |  |  | $59.2 |
(a) | In 2019, Alliant Energy and IPL recognized additional AROs related to IPL’s newly constructed Upland Prairie and English Farms wind sites. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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