XML 60 R37.htm IDEA: XBRL DOCUMENT
v3.20.2

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2020 | Jun. 30, 2019
Regulatory Matters [Line Items] |  |  |
Credits issued to customers |  | $ (63.4) | $ (26.1)
Electric transmission cost recovery [Member] | IPL [Member] |  |  |
Regulatory Matters [Line Items] |  |  |
Credits issued to customers | $ 42.0 |  |

X
- Definition Regulatory Matters [Line Items] + References No definition available. + Details
Name: | lnt_RegulatoryMattersLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInRegulatoryLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RegulatoryLiabilityAxis=lnt_ElectricTransmissionCostRecoveryMember
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: |