XML 109 R76.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Preferred Stock (Narrative) (Details) - IPL [Member] | 12 Months Ended
--- | ---
Dec. 31, 2018 Q board_member $ / shares shares | Dec. 31, 2017 shares
Temporary Equity [Line Items] |  |
Number of board members to be elected (in members) | board_member | 2 |
Number of quarterly dividend requirements (in quarters) | Q | 6 |
Redeemable Preferred Stock [Member] |  |
Temporary Equity [Line Items] |  |
Shares Authorized (in shares) | 16,000,000 |
Redeemable Preferred Stock [Member] | 5.1% [Member] |  |
Temporary Equity [Line Items] |  |
Shares Authorized (in shares) | 8,000,000 | 8,000,000
Cumulative preferred stock rate | 5.10% | 5.10%
Preferred stock redemption price per share (in dollars per share) | $ / shares | $ 25 |

X
- Definition Number of board members to be elected if preferred dividends are in arrears for specified amount of time + References No definition available. + Details
Name: | lnt_NumberOfBoardMembersToBeElected
Namespace Prefix: | lnt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number Of Quarterly Dividend Requirements + References No definition available. + Details
Name: | lnt_NumberOfQuarterlyDividendRequirements
Namespace Prefix: | lnt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage rate used to calculate dividend payments on preferred stock. + References No definition available. + Details
Name: | us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity is redeemed or may be called at. The redemption features of this preferred stock are solely within the control 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 3 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644 Reference 2: 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=84159872&loc=d3e21564-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21488-112644 + Details
Name: | us-gaap_PreferredStockRedemptionPricePerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws. + References Reference 1: 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_PreferredStockSharesAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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

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

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=us-gaap_RedeemablePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | lnt_RedeemablePreferredStockByDividendRateAxis=lnt_FivePointOnePercentageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |