v2.4.0.6

Asset Retirement Obligations (AROs) (Tables) | 9 Months Ended
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Sep. 30, 2012
Asset Retirement Obligation Disclosure [Abstract] |
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
| 2012 |  | 2011 |  | 2012 |  | 2011 |  | 2012 |  | 2011
Balance, January 1 |  | $91.1 |  |  |  | $75.9 |  |  |  | $56.2 |  |  |  | $43.6 |  |  |  | $34.9 |  |  |  | $32.3 |
Revisions in estimated cash flows (a) | (9.9 | ) |  | 7.8 |  |  | (9.2 | ) |  | 7.7 |  |  | (0.7 | ) |  | 0.1 |
Liabilities settled | (2.6 | ) |  | (0.5 | ) |  | (2.5 | ) |  | (0.4 | ) |  | (0.1 | ) |  | (0.1 | )
Liabilities incurred (b) | 16.0 |  |  | 4.0 |  |  | — |  |  | 3.1 |  |  | 7.6 |  |  | 0.9 |
Accretion expense | 2.6 |  |  | 3.4 |  |  | 1.4 |  |  | 2.1 |  |  | 1.2 |  |  | 1.3 |
Balance, September 30 |  | $97.2 |  |  |  | $90.6 |  |  |  | $45.9 |  |  |  | $56.1 |  |  |  | $42.9 |  |  |  | $34.5 |
(a) | For the nine months ended September 30, 2012 and 2011, IPL recorded revisions in estimated cash flows of ($8.2) million and $7.0 million, respectively, based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
(b) | For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to its Nelson Dewey 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 -Topic 410 -SubTopic 30 -Publisher FASB -Number -Article -Subparagraph -Name Accounting Standards Codification -Paragraph 5 -Section 50 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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