v2.4.0.6

Asset Retirement Obligations (AROs) | 9 Months Ended
--- | ---
Sep. 30, 2012
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
| 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.
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
| 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.
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
| 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.

X
- Details
Name: | lnt_AssetRetirementObligationsLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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 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. 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 Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
Name: | us-gaap_AssetRetirementObligationDisclosureTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration