XML 74 R51.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Income Taxes (Narrative) (Details) $ in Millions | 6 Months Ended
--- | ---
Jun. 30, 2017 USD ($)
Income Taxes [Line Items] |
Increase in deferred tax liabilities | $ 111.1
IPL [Member] |
Income Taxes [Line Items] |
Increase in deferred tax liabilities | 75.1
WPL [Member] |
Income Taxes [Line Items] |
Increase in deferred tax liabilities | $ 28.4

X
- Definition Income tax + References No definition available. + Details
Name: | lnt_IncomeTaxLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Increase Decrease In Deferred Income Taxes Noncurrent Liabilities + References No definition available. + Details
Name: | lnt_IncreaseDecreaseInDeferredIncomeTaxesNoncurrentLiabilities
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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: |