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Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details) - $ / shares | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Performance Shares [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 223,511 | 257,599
Performance Units [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 73,240 | 93,320
2017 Grant [Member] | Performance Shares [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 65,350 |
Alliant Energy common stock closing price on September 29, 2017 (in dollars per share) | $ 41.57 |
Estimated payout percentage based on performance criteria | 100.00% |
Fair values of each nonvested award (in dollars per share) | $ 41.57 |
2017 Grant [Member] | Performance Units [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 19,531 |
Alliant Energy common stock closing price on September 29, 2017 (in dollars per share) | $ 41.57 |
Estimated payout percentage based on performance criteria | 100.00% |
Fair values of each nonvested award (in dollars per share) | $ 41.57 |
2016 Grant [Member] | Performance Shares [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 67,355 |
Alliant Energy common stock closing price on September 29, 2017 (in dollars per share) | $ 41.57 |
Estimated payout percentage based on performance criteria | 138.00% |
Fair values of each nonvested award (in dollars per share) | $ 57.37 |
2016 Grant [Member] | Performance Units [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 21,751 |
Alliant Energy common stock closing price on September 29, 2017 (in dollars per share) | $ 41.57 |
Estimated payout percentage based on performance criteria | 138.00% |
Fair values of each nonvested award (in dollars per share) | $ 57.37 |
2015 Grant [Member] | Performance Shares [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 90,806 |
Alliant Energy common stock closing price on September 29, 2017 (in dollars per share) | $ 41.57 |
Estimated payout percentage based on performance criteria | 113.00% |
Fair values of each nonvested award (in dollars per share) | $ 46.97 |
2015 Grant [Member] | Performance Units [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Nonvested awards at target (in shares/awards) | 31,958 |
Alliant Energy common stock closing price on grant date (in dollars per share) | $ 32.55 |
Estimated payout percentage based on performance criteria | 113.00% |
Fair values of each nonvested award (in dollars per share) | $ 36.78 |

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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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