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Redeemable Preferred Stock (Carrying Value Of Cumulative Preferred Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012
Temporary Equity [Line Items] |  |  |  |
Cumulative preferred stock | $ 200.0 |  | $ 145.1 |
Cumulative preferred stock | 0 |  | 60.0 |
Redeemable Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Cumulative preferred stock | 200.0 |  | 205.1 |
IPL [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Authorized shares (in shares) | 16,000,000 |  | 16,000,000 |
Cumulative preferred stock rate | 5.10% |  | 8.375% |
Cumulative preferred stock | 200.0 |  | 145.1 |
IPL [Member] | Redeemable Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Cumulative preferred stock | 200.0 |  | 145.1 |
Less: discount | 0 |  | (4.9) |
WPL [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Authorized shares (in shares) | 16,000,000 |  | 3,750,000 |
Cumulative preferred stock rate |  |  | 4.50% |
Cumulative preferred stock | 0 |  | 60.0 |
5.1% [Member] | IPL [Member] | Redeemable Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Liquidation Preference/Stated Value (in dollars per share) | $ 25 |  |  |
Shares outstanding (in shares) | 8,000,000 |  |  |
Cumulative preferred stock rate | 5.10% |  |  |
Redemption (none are mandatorily redeemable) | On or after March 15, 2018 |  |  |
Cumulative preferred stock | 200.0 |  | 0 |
8.375% [Member] | IPL [Member] | Redeemable Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Liquidation Preference/Stated Value (in dollars per share) |  |  | $ 25 | [1]
Shares outstanding (in shares) |  |  | 6,000,000 | [1]
Cumulative preferred stock rate | 8.375% |  | 8.375% | [1]
Cumulative preferred stock | 0 | [1] | 150.0 | [1]
Preferred stock redeemed during period (in shares) | 6,000,000 |  |  |
Preferred stock redeemed during period, value | 150 |  |  |
8.375% [Member] | Alliant Energy and IPL [Member] | Redeemable Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Preferred stock redemption charge | 5 |  |  |
4.40% through 6.50% [Member] | WPL [Member] | Redeemable Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Shares outstanding (in shares) |  |  | 1,049,225 | [2]
Cumulative preferred stock | 0 | [2] | 60.0 | [2]
Preferred stock redeemed during period (in shares) | 1,049,225 |  |  |
Preferred stock redeemed during period, value | 61 |  |  |
4.40% through 6.50% [Member] | Alliant Energy and WPL [Member] | Redeemable Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Preferred stock redemption charge | $ 1 |  |  |
Maximum [Member] | WPL [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Liquidation Preference/Stated Value (in dollars per share) |  |  | $ 100 | [2]
Cumulative preferred stock rate | 6.50% | [2] |  |
Minimum [Member] | WPL [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Liquidation Preference/Stated Value (in dollars per share) |  |  | $ 25 | [2]
Cumulative preferred stock rate | 4.40% | [2] |  |
[1] | In 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge in 2013 related to this transaction in “Preferred dividend requirements” in their Consolidated Statements of Income.
[2] | In 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and WPL recorded a $1 million charge in 2013 related to this transaction in “Preferred dividend requirements” in their Consolidated Statements of Income.

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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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- 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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- Definition The excess of (1) the carrying amount of the preferred stock in the registrant's balance sheet over (2) the fair value of the consideration transferred to the holders of the preferred stock, during the accounting period, which will be added to net earnings to arrive at net earnings available to common shareholders in the calculation of earnings per share. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section S99 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=27010884&loc=d3e42851-122695 + Details
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- Definition The excess of (1) fair value of the consideration transferred to the holders of the preferred stock over (2) the carrying amount of the preferred stock in the registrant's balance sheet, during the accounting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section S99 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=27010884&loc=d3e42851-122695 + Details
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- Definition The redemption terms of 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. The redemption features of this capital 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=6928386&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=6928386&loc=d3e21564-112644 + Details
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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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- 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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- Definition Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer. + References No definition available. + Details
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