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Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details) | 12 Months Ended
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Dec. 31, 2017 $ / shares shares
Performance Shares [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 223,511
Performance Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 71,737
2017 Grant [Member] | Performance Shares [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 65,350
Alliant Energy common stock closing price on December 29, 2017 (in dollars per share) | $ 42.61
Estimated payout percentage based on performance criteria | 105.00%
Fair values of each nonvested award (in dollars per share) | $ 44.74
2017 Grant [Member] | Performance Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 18,600
Alliant Energy common stock closing price on December 29, 2017 (in dollars per share) | $ 42.61
Estimated payout percentage based on performance criteria | 105.00%
Fair values of each nonvested award (in dollars per share) | $ 44.74
2016 Grant [Member] | Performance Shares [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 67,355
Alliant Energy common stock closing price on December 29, 2017 (in dollars per share) | $ 42.61
Estimated payout percentage based on performance criteria | 150.00%
Fair values of each nonvested award (in dollars per share) | $ 63.92
2016 Grant [Member] | Performance Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 21,227
Alliant Energy common stock closing price on December 29, 2017 (in dollars per share) | $ 42.61
Estimated payout percentage based on performance criteria | 150.00%
Fair values of each nonvested award (in dollars per share) | $ 63.92
2015 Grant [Member] | Performance Shares [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 90,806
Alliant Energy common stock closing price on December 29, 2017 (in dollars per share) | $ 42.61
Estimated payout percentage based on performance criteria | 138.00%
Fair values of each nonvested award (in dollars per share) | $ 58.80
2015 Grant [Member] | Performance Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Nonvested, December 31 (in shares/awards) | shares | 31,910
Alliant Energy common stock closing price on grant date (in dollars per share) | $ 32.55
Estimated payout percentage based on performance criteria | 138.00%
Fair values of each nonvested award (in dollars per share) | $ 44.92

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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 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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