XML 60 R37.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Regulatory Matters (Tax Benefit Riders) (Details) - USD ($) $ in Millions | 6 Months Ended
--- | ---
Jun. 30, 2017 | Jun. 30, 2016
Regulatory Liabilities [Line Items] |  |
Decrease in regulatory liabilities | $ (19.0) | $ (29.2)
Alliant Energy and IPL [Member] | Electric tax benefit rider [Member] |  |
Regulatory Liabilities [Line Items] |  |
Decrease in regulatory liabilities | (33.0) |
Alliant Energy and IPL [Member] | Gas tax benefit rider [Member] |  |
Regulatory Liabilities [Line Items] |  |
Decrease in regulatory liabilities | (3.0) |
Alliant Energy and IPL [Member] | Tax benefit riders [Member] |  |
Regulatory Liabilities [Line Items] |  |
Decrease in regulatory liabilities | $ (36.0) |

X
- Definition The increase (decrease) during the reporting period in regulated liabilities. Regulated liabilities are created when regulatory agency permits an entity to defer revenues to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInRegulatoryLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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_RegulatoryLiabilitiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=lnt_ElectricTaxBenefitRiderMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=lnt_GasTaxBenefitRiderMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=lnt_TaxBenefitRiderMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |