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Redeemable Preferred Stock Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified | 6 Months Ended | 1 Months Ended | 6 Months Ended | 1 Months Ended | 6 Months Ended
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Jun. 30, 2014 IPL [Member] | Mar. 31, 2013 IPL [Member] Redeemable Preferred Stock [Member] 8.375% [Member] | Jun. 30, 2013 Alliant Energy and IPL [Member] Redeemable Preferred Stock [Member] | Mar. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 4.40% through 6.50% [Member] | Mar. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 4.40% [Member] | Mar. 31, 2013 WPL [Member] Redeemable Preferred Stock [Member] 6.50% [Member] | Jun. 30, 2013 Alliant Energy and WPL [Member] Redeemable Preferred Stock [Member] 4.40% through 6.50% [Member]
Temporary Equity [Line Items] |  |  |  |  |  |  |
Preferred stock redeemed during period (in shares) |  | 6,000,000 |  | 1,049,225 |  |  |
Preferred stock series | 5.10% | 8.375% |  |  | 4.40% | 6.50% |
Preferred stock redeemed during period, value |  | $ 150 |  | $ 61 |  |  |
Preferred stock redemption charge |  |  | $ 5 |  |  |  | $ 1

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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 Number of stock bought back by the entity at the exercise price or redemption price. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 + Details
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- Definition Equity impact of the value of stock bought back by the entity at the exercise price or redemption price. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 + Details
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