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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2017
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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Balance, January 1 |  | $195.7 |  |  |  | $214.0 |  |  |  | $124.7 |  |  |  | $132.9 |  |  |  | $61.4 |  |  |  | $71.9 |
Revisions in estimated cash flows | 4.3 |  |  | (13.3 | ) |  | 7.0 |  |  | (5.8 | ) |  | (2.7 | ) |  | (7.5 | )
Liabilities settled | (23.5 | ) |  | (14.0 | ) |  | (13.1 | ) |  | (6.8 | ) |  | (10.4 | ) |  | (7.2 | )
Liabilities incurred | 2.0 |  |  | 2.6 |  |  | 11.7 |  |  | 0.7 |  |  | — |  |  | 1.9 |
Accretion expense | 6.0 |  |  | 6.4 |  |  | 3.8 |  |  | 3.7 |  |  | 2.1 |  |  | 2.3 |
Balance, December 31 |  | $184.5 |  |  |  | $195.7 |  |  |  | $134.1 |  |  |  | $124.7 |  |  |  | $50.4 |  |  |  | $61.4 |
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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Balance, January 1 |  | $195.7 |  |  |  | $214.0 |  |  |  | $124.7 |  |  |  | $132.9 |  |  |  | $61.4 |  |  |  | $71.9 |
Revisions in estimated cash flows | 4.3 |  |  | (13.3 | ) |  | 7.0 |  |  | (5.8 | ) |  | (2.7 | ) |  | (7.5 | )
Liabilities settled | (23.5 | ) |  | (14.0 | ) |  | (13.1 | ) |  | (6.8 | ) |  | (10.4 | ) |  | (7.2 | )
Liabilities incurred | 2.0 |  |  | 2.6 |  |  | 11.7 |  |  | 0.7 |  |  | — |  |  | 1.9 |
Accretion expense | 6.0 |  |  | 6.4 |  |  | 3.8 |  |  | 3.7 |  |  | 2.1 |  |  | 2.3 |
Balance, December 31 |  | $184.5 |  |  |  | $195.7 |  |  |  | $134.1 |  |  |  | $124.7 |  |  |  | $50.4 |  |  |  | $61.4 |
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
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Balance, January 1 |  | $195.7 |  |  |  | $214.0 |  |  |  | $124.7 |  |  |  | $132.9 |  |  |  | $61.4 |  |  |  | $71.9 |
Revisions in estimated cash flows | 4.3 |  |  | (13.3 | ) |  | 7.0 |  |  | (5.8 | ) |  | (2.7 | ) |  | (7.5 | )
Liabilities settled | (23.5 | ) |  | (14.0 | ) |  | (13.1 | ) |  | (6.8 | ) |  | (10.4 | ) |  | (7.2 | )
Liabilities incurred | 2.0 |  |  | 2.6 |  |  | 11.7 |  |  | 0.7 |  |  | — |  |  | 1.9 |
Accretion expense | 6.0 |  |  | 6.4 |  |  | 3.8 |  |  | 3.7 |  |  | 2.1 |  |  | 2.3 |
Balance, December 31 |  | $184.5 |  |  |  | $195.7 |  |  |  | $134.1 |  |  |  | $124.7 |  |  |  | $50.4 |  |  |  | $61.4 |

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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://www.xbrl.org/2003/role/presentationRef -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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