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v2.4.1.9

Redeemable Preferred Stock (Carrying Value Of Cumulative Preferred Stock) (Details) (IPL [Member], USD $) In Millions, except Share data, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Temporary Equity [Line Items] |  |
Series | 5.10%us-gaap_PreferredStockDividendRatePercentage |
Redeemable Preferred Stock [Member] |  |
Temporary Equity [Line Items] |  |
Shares Authorized (in shares) | 16,000,000 us-gaap_PreferredStockSharesAuthorized / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementClassOfStockAxis = us-gaap_RedeemablePreferredStockMember |
5.1% [Member] | Redeemable Preferred Stock [Member] |  |
Temporary Equity [Line Items] |  |
Liquidation Preference/Stated Value (in dollars per share) | $ 25 us-gaap_PreferredStockParOrStatedValuePerShare / dei_LegalEntityAxis = lnt_IplMember / lnt_RedeemablePreferredStockByDividendRateAxis = lnt_FivePointOnePercentageMember / us-gaap_StatementClassOfStockAxis = us-gaap_RedeemablePreferredStockMember |
Shares Outstanding (in shares) | 8,000,000 us-gaap_PreferredStockSharesOutstanding / dei_LegalEntityAxis = lnt_IplMember / lnt_RedeemablePreferredStockByDividendRateAxis = lnt_FivePointOnePercentageMember / us-gaap_StatementClassOfStockAxis = us-gaap_RedeemablePreferredStockMember |
Series | 5.10%us-gaap_PreferredStockDividendRatePercentage / dei_LegalEntityAxis = lnt_IplMember / lnt_RedeemablePreferredStockByDividendRateAxis = lnt_FivePointOnePercentageMember / us-gaap_StatementClassOfStockAxis = us-gaap_RedeemablePreferredStockMember | 5.10%us-gaap_PreferredStockDividendRatePercentage / dei_LegalEntityAxis = lnt_IplMember / lnt_RedeemablePreferredStockByDividendRateAxis = lnt_FivePointOnePercentageMember / us-gaap_StatementClassOfStockAxis = us-gaap_RedeemablePreferredStockMember
Cumulative preferred stock | $ 200.0 us-gaap_PreferredStockValue / dei_LegalEntityAxis = lnt_IplMember / lnt_RedeemablePreferredStockByDividendRateAxis = lnt_FivePointOnePercentageMember / us-gaap_StatementClassOfStockAxis = us-gaap_RedeemablePreferredStockMember | $ 200.0 us-gaap_PreferredStockValue / dei_LegalEntityAxis = lnt_IplMember / lnt_RedeemablePreferredStockByDividendRateAxis = lnt_FivePointOnePercentageMember / us-gaap_StatementClassOfStockAxis = us-gaap_RedeemablePreferredStockMember

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

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- Definition Face amount or stated value per share of preferred stock nonredeemable or 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 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29 -Article 5 + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

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- 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29 -Article 5 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Definition Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased. + 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29 -Article 5 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | instant

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- Definition Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 3: 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 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29 -Article 5 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_TemporaryEquityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |