XML 57 R30.htm IDEA: XBRL DOCUMENT
v3.2.0.727

Asset Retirement Obligations (Tables) | 6 Months Ended
--- | ---
Jun. 30, 2015
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
| 2015 |  | 2014 |  | 2015 |  | 2014 |  | 2015 |  | 2014
Balance, January 1 |  | $114.0 |  |  |  | $109.7 |  |  |  | $51.8 |  |  |  | $47.9 |  |  |  | $52.4 |  |  |  | $52.4 |
Revisions in estimated cash flows (a) | 2.1 |  |  | — |  |  | 0.9 |  |  | — |  |  | 1.2 |  |  | — |
Liabilities settled | (6.4 | ) |  | (0.7 | ) |  | (2.4 | ) |  | (0.4 | ) |  | (4.0 | ) |  | (0.3 | )
Liabilities incurred (a) | 72.3 |  |  | 16.5 |  |  | 56.1 |  |  | 16.3 |  |  | 16.2 |  |  | 0.2 |
Accretion expense | 2.2 |  |  | 2.1 |  |  | 0.9 |  |  | 1.0 |  |  | 0.9 |  |  | 0.8 |
Balance, June 30 |  | $184.2 |  |  |  | $127.6 |  |  |  | $107.3 |  |  |  | $64.8 |  |  |  | $66.7 |  |  |  | $53.1 |
(a) | In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. In the second quarter of 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million, $57 million and $17 million, respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in “Property, plant and equipment, net” on the respective balance sheets. Actual costs resulting from the CCR rule may be different than the amounts recorded in the second quarter of 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.
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
| 2015 |  | 2014 |  | 2015 |  | 2014 |  | 2015 |  | 2014
Balance, January 1 |  | $114.0 |  |  |  | $109.7 |  |  |  | $51.8 |  |  |  | $47.9 |  |  |  | $52.4 |  |  |  | $52.4 |
Revisions in estimated cash flows (a) | 2.1 |  |  | — |  |  | 0.9 |  |  | — |  |  | 1.2 |  |  | — |
Liabilities settled | (6.4 | ) |  | (0.7 | ) |  | (2.4 | ) |  | (0.4 | ) |  | (4.0 | ) |  | (0.3 | )
Liabilities incurred (a) | 72.3 |  |  | 16.5 |  |  | 56.1 |  |  | 16.3 |  |  | 16.2 |  |  | 0.2 |
Accretion expense | 2.2 |  |  | 2.1 |  |  | 0.9 |  |  | 1.0 |  |  | 0.9 |  |  | 0.8 |
Balance, June 30 |  | $184.2 |  |  |  | $127.6 |  |  |  | $107.3 |  |  |  | $64.8 |  |  |  | $66.7 |  |  |  | $53.1 |
(a) | In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. In the second quarter of 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million, $57 million and $17 million, respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in “Property, plant and equipment, net” on the respective balance sheets. Actual costs resulting from the CCR rule may be different than the amounts recorded in the second quarter of 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.
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
| 2015 |  | 2014 |  | 2015 |  | 2014 |  | 2015 |  | 2014
Balance, January 1 |  | $114.0 |  |  |  | $109.7 |  |  |  | $51.8 |  |  |  | $47.9 |  |  |  | $52.4 |  |  |  | $52.4 |
Revisions in estimated cash flows (a) | 2.1 |  |  | — |  |  | 0.9 |  |  | — |  |  | 1.2 |  |  | — |
Liabilities settled | (6.4 | ) |  | (0.7 | ) |  | (2.4 | ) |  | (0.4 | ) |  | (4.0 | ) |  | (0.3 | )
Liabilities incurred (a) | 72.3 |  |  | 16.5 |  |  | 56.1 |  |  | 16.3 |  |  | 16.2 |  |  | 0.2 |
Accretion expense | 2.2 |  |  | 2.1 |  |  | 0.9 |  |  | 1.0 |  |  | 0.9 |  |  | 0.8 |
Balance, June 30 |  | $184.2 |  |  |  | $127.6 |  |  |  | $107.3 |  |  |  | $64.8 |  |  |  | $66.7 |  |  |  | $53.1 |
(a) | In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. In the second quarter of 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million, $57 million and $17 million, respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in “Property, plant and equipment, net” on the respective balance sheets. Actual costs resulting from the CCR rule may be different than the amounts recorded in the second quarter of 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.

X
- Definition [Line Items] for Schedule of Asset Retirement Obligations [Table] + References No definition available. + Details
Name: | lnt_ScheduleOfAssetRetirementObligationsLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_ScheduleOfChangeInAssetRetirementObligationTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |