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Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) (USD $) |  |  |  |  |  |  |  |  | 9 Months Ended
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Sep. 30, 2014 Performance Shares [Member] | Dec. 31, 2013 Performance Shares [Member] | Sep. 30, 2013 Performance Shares [Member] | Dec. 31, 2012 Performance Shares [Member] | Sep. 30, 2014 Performance Units [Member] | Dec. 31, 2013 Performance Units [Member] | Sep. 30, 2013 Performance Units [Member] | Dec. 31, 2012 Performance Units [Member] | Sep. 30, 2014 2014 Grant [Member] Performance Shares [Member] | Sep. 30, 2014 2014 Grant [Member] Performance Units [Member] | Sep. 30, 2014 2013 Grant [Member] Performance Shares [Member] | Sep. 30, 2014 2013 Grant [Member] Performance Units [Member] | Sep. 30, 2014 2012 Grant [Member] Performance Shares [Member] | Sep. 30, 2014 2012 Grant [Member] Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nonvested awards (in shares/awards) | 144,424 | 139,940 | 139,940 | 145,277 | 64,625 | 65,912 | 65,912 | 64,969 | 49,719 | 19,775 | 49,093 | 21,726 | 45,612 | 23,124
Alliant Energy common stock closing price on September 30, 2014 (in dollars per share) |  |  |  |  |  |  |  |  | $ 55.41 |  | $ 55.41 |  | $ 55.41 |
Alliant Energy common stock closing price on grant date (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 53.77 |  | $ 47.58 |  | $ 43.05
Estimated payout percentage based on performance criteria |  |  |  |  |  |  |  |  | 94.00% | 94.00% | 117.00% | 117.00% | 126.00% | 126.00%
Fair values of each nonvested award (in dollars per share) |  |  |  |  |  |  |  |  | $ 52.09 | $ 50.54 | $ 64.83 | $ 55.67 | $ 69.82 | $ 54.24

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- Definition Common Stock Closing Price Grant Date + References No definition available. + Details
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- Definition Employee Service Share Based Compensation Fair Values Of Each Nonvested Awards + References No definition available. + Details
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- Definition Estimated Payout Percentage + References No definition available. + Details
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- Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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