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Asset Retirement Obligations (AROs) | 3 Months Ended
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Mar. 31, 2013
Asset Retirement Obligations [Line Items] |
Asset Retirement Obligations (AROs) | 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] |
Asset Retirement Obligations [Line Items] |
Asset Retirement Obligations (AROs) | 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] |
Asset Retirement Obligations [Line Items] |
Asset Retirement Obligations (AROs) | 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 The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7569-110849 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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