XML 142 R110.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Benefit Plans (Estimated Future Funding) (Details) - Scenario, Forecast [Member] $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 USD ($)
Defined Benefit Pension Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Estimated funding for calendar year 2016 | $ 2.6 | [1]
Defined Benefit Pension Plans [Member] | IPL [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Estimated funding for calendar year 2016 | 0.8 | [1]
Defined Benefit Pension Plans [Member] | WPL [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Estimated funding for calendar year 2016 | 0.1 | [1]
Other Postretirement Benefits Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Estimated funding for calendar year 2016 | 5.8 |
Other Postretirement Benefits Plans [Member] | IPL [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Estimated funding for calendar year 2016 | 0.0 |
Other Postretirement Benefits Plans [Member] | WPL [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Estimated funding for calendar year 2016 | $ 5.5 |
[1] | Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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: |

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |