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Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) - $ / shares | 6 Months Ended |  |  |
--- | --- | --- | --- | ---
Jun. 30, 2016 | Dec. 31, 2015 | Jun. 30, 2015 | Dec. 31, 2014
Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 257,599 | 288,430 | 288,430 | 288,848
Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 93,431 | 116,412 | 116,648 | 127,330
2016 Grant [Member] | Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 67,355 |  |  |
Alliant Energy common stock closing price on June 30, 2016 (in dollars per share) | $ 39.70 |  |  |
Estimated payout percentage based on performance criteria | 118.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 46.85 |  |  |
2016 Grant [Member] | Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 22,768 |  |  |
Alliant Energy common stock closing price on June 30, 2016 (in dollars per share) | $ 39.70 |  |  |
Estimated payout percentage based on performance criteria | 118.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 46.85 |  |  |
2015 Grant [Member] | Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 90,806 |  |  |
Alliant Energy common stock closing price on June 30, 2016 (in dollars per share) | $ 39.70 |  |  |
Estimated payout percentage based on performance criteria | 150.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 59.55 |  |  |
2015 Grant [Member] | Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 33,268 |  |  |
Alliant Energy common stock closing price on grant date (in dollars per share) | $ 32.55 |  |  |
Estimated payout percentage based on performance criteria | 150.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 48.82 |  |  |
2014 Grant [Member] | Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 99,438 |  |  |
Alliant Energy common stock closing price on June 30, 2016 (in dollars per share) | $ 39.70 |  |  |
Estimated payout percentage based on performance criteria | 155.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 61.54 |  |  |
2014 Grant [Member] | Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 37,395 |  |  |
Alliant Energy common stock closing price on grant date (in dollars per share) | $ 26.89 |  |  |
Estimated payout percentage based on performance criteria | 155.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 41.67 |  |  |

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