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Asset Retirement Obligations (AROs) (Tables) | 3 Months Ended
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Mar. 31, 2013
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
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Balance, January 1 |  | $101.5 |  |  |  | $91.1 |  |  |  | $45.5 |  |  |  | $56.2 |  |  |  | $46.9 |  |  |  | $34.9 |
Revisions in estimated cash flows (a) | — |  |  | (8.2 | ) |  | — |  |  | (8.2 | ) |  | — |  |  | — |
Liabilities settled | (0.1 | ) |  | (1.0 | ) |  | — |  |  | (0.9 | ) |  | (0.1 | ) |  | (0.1 | )
Accretion expense | 1.0 |  |  | 0.9 |  |  | 0.5 |  |  | 0.5 |  |  | 0.4 |  |  | 0.4 |
Balance, March 31 |  | $102.4 |  |  |  | $82.8 |  |  |  | $46.0 |  |  |  | $47.6 |  |  |  | $47.2 |  |  |  | $35.2 |
(a) | For the three months ended March 31, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
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
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Balance, January 1 |  | $101.5 |  |  |  | $91.1 |  |  |  | $45.5 |  |  |  | $56.2 |  |  |  | $46.9 |  |  |  | $34.9 |
Revisions in estimated cash flows (a) | — |  |  | (8.2 | ) |  | — |  |  | (8.2 | ) |  | — |  |  | — |
Liabilities settled | (0.1 | ) |  | (1.0 | ) |  | — |  |  | (0.9 | ) |  | (0.1 | ) |  | (0.1 | )
Accretion expense | 1.0 |  |  | 0.9 |  |  | 0.5 |  |  | 0.5 |  |  | 0.4 |  |  | 0.4 |
Balance, March 31 |  | $102.4 |  |  |  | $82.8 |  |  |  | $46.0 |  |  |  | $47.6 |  |  |  | $47.2 |  |  |  | $35.2 |
(a) | For the three months ended March 31, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
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
| 2013 |  | 2012 |  | 2013 |  | 2012 |  | 2013 |  | 2012
Balance, January 1 |  | $101.5 |  |  |  | $91.1 |  |  |  | $45.5 |  |  |  | $56.2 |  |  |  | $46.9 |  |  |  | $34.9 |
Revisions in estimated cash flows (a) | — |  |  | (8.2 | ) |  | — |  |  | (8.2 | ) |  | — |  |  | — |
Liabilities settled | (0.1 | ) |  | (1.0 | ) |  | — |  |  | (0.9 | ) |  | (0.1 | ) |  | (0.1 | )
Accretion expense | 1.0 |  |  | 0.9 |  |  | 0.5 |  |  | 0.5 |  |  | 0.4 |  |  | 0.4 |
Balance, March 31 |  | $102.4 |  |  |  | $82.8 |  |  |  | $46.0 |  |  |  | $47.6 |  |  |  | $47.2 |  |  |  | $35.2 |
(a) | For the three months ended March 31, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.

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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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