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Asset Retirement Obligations (Tables) | 3 Months Ended
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Mar. 31, 2016
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Balance, January 1 |  | $214.0 |  |  |  | $114.0 |  |  |  | $132.9 |  |  |  | $51.8 |  |  |  | $71.9 |  |  |  | $52.4 |
Revisions in estimated cash flows | 0.5 |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
Liabilities settled | (2.7 | ) |  | (2.2 | ) |  | (0.7 | ) |  | (2.2 | ) |  | (2.0 | ) |  | — |
Liabilities incurred | 0.7 |  |  | — |  |  | 0.7 |  |  | — |  |  | — |  |  | — |
Accretion expense | 1.6 |  |  | 1.0 |  |  | 0.9 |  |  | 0.4 |  |  | 0.6 |  |  | 0.4 |
Balance, March 31 |  | $214.1 |  |  |  | $112.8 |  |  |  | $134.3 |  |  |  | $50.0 |  |  |  | $70.5 |  |  |  | $52.8 |
IPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Balance, January 1 |  | $214.0 |  |  |  | $114.0 |  |  |  | $132.9 |  |  |  | $51.8 |  |  |  | $71.9 |  |  |  | $52.4 |
Revisions in estimated cash flows | 0.5 |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
Liabilities settled | (2.7 | ) |  | (2.2 | ) |  | (0.7 | ) |  | (2.2 | ) |  | (2.0 | ) |  | — |
Liabilities incurred | 0.7 |  |  | — |  |  | 0.7 |  |  | — |  |  | — |  |  | — |
Accretion expense | 1.6 |  |  | 1.0 |  |  | 0.9 |  |  | 0.4 |  |  | 0.6 |  |  | 0.4 |
Balance, March 31 |  | $214.1 |  |  |  | $112.8 |  |  |  | $134.3 |  |  |  | $50.0 |  |  |  | $70.5 |  |  |  | $52.8 |
WPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Balance, January 1 |  | $214.0 |  |  |  | $114.0 |  |  |  | $132.9 |  |  |  | $51.8 |  |  |  | $71.9 |  |  |  | $52.4 |
Revisions in estimated cash flows | 0.5 |  |  | — |  |  | 0.5 |  |  | — |  |  | — |  |  | — |
Liabilities settled | (2.7 | ) |  | (2.2 | ) |  | (0.7 | ) |  | (2.2 | ) |  | (2.0 | ) |  | — |
Liabilities incurred | 0.7 |  |  | — |  |  | 0.7 |  |  | — |  |  | — |  |  | — |
Accretion expense | 1.6 |  |  | 1.0 |  |  | 0.9 |  |  | 0.4 |  |  | 0.6 |  |  | 0.4 |
Balance, March 31 |  | $214.1 |  |  |  | $112.8 |  |  |  | $134.3 |  |  |  | $50.0 |  |  |  | $70.5 |  |  |  | $52.8 |

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- Definition [Line Items] for Schedule of Asset Retirement Obligations [Table] + References No definition available. + Details
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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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