XML 71 R37.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Redeemable Preferred Stock (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2017
Class of Stock [Line Items] |
Schedule of Carrying Value of Cumulative Preferred Stock | Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows:
Series |  | Liquidation Preference/Stated Value |  | Shares Authorized |  | Shares Outstanding |  | 2017 |  | 2016
|  |  |  |  |  |  |  | (in millions)
5.1% |  | $25 |  | 8,000,000 |  | 8,000,000 |  |  | $200.0 |  |  |  | $200.0 |
IPL [Member] |
Class of Stock [Line Items] |
Schedule of Carrying Value of Cumulative Preferred Stock | Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows:
Series |  | Liquidation Preference/Stated Value |  | Shares Authorized |  | Shares Outstanding |  | 2017 |  | 2016
|  |  |  |  |  |  |  | (in millions)
5.1% |  | $25 |  | 8,000,000 |  | 8,000,000 |  |  | $200.0 |  |  |  | $200.0 |

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

X
- Definition Tabular disclosure of information pertaining to auction market preferred securities, including liquidation preference, liquidation value, par value, rate setting interval, redemption requirements, dividend distributions, roll forward of shares outstanding, shares authorized, aggregate value of auction market preferred securities, variable interest rate earned, and other information necessary to a fair presentation. If redeemable, the auction market preferred securities are redeemable solely at the option of the issuer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_ScheduleOfAuctionMarketPreferredSecuritiesByStockSeriesTextBlock
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: |