XML 81 R61.htm IDEA: XBRL DOCUMENT
v3.4.0.3

Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) - $ / shares | 3 Months Ended |  |  |
--- | --- | --- | --- | ---
Mar. 31, 2016 | Dec. 31, 2015 | Mar. 31, 2015 | Dec. 31, 2014
Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 128,283 | 144,215 | 144,215 | 144,424
Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 48,403 | 58,206 | 58,564 | 63,665
2016 Grant [Member] | Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 33,161 |  |  |
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share) | $ 74.28 |  |  |
Estimated payout percentage based on performance criteria | 108.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 80.22 |  |  |
2016 Grant [Member] | Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 11,959 |  |  |
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share) | $ 74.28 |  |  |
Estimated payout percentage based on performance criteria | 108.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 80.22 |  |  |
2015 Grant [Member] | Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 45,403 |  |  |
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share) | $ 74.28 |  |  |
Estimated payout percentage based on performance criteria | 90.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 66.85 |  |  |
2015 Grant [Member] | Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 17,209 |  |  |
Alliant Energy common stock closing price on grant date (in dollars per share) | $ 65.09 |  |  |
Estimated payout percentage based on performance criteria | 90.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 58.58 |  |  |
2014 Grant [Member] | Performance Shares [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 49,719 |  |  |
Alliant Energy common stock closing price on March 31, 2016 (in dollars per share) | $ 74.28 |  |  |
Estimated payout percentage based on performance criteria | 138.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 102.51 |  |  |
2014 Grant [Member] | Performance Units [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Nonvested awards (in shares/awards) | 19,235 |  |  |
Alliant Energy common stock closing price on grant date (in dollars per share) | $ 53.77 |  |  |
Estimated payout percentage based on performance criteria | 138.00% |  |  |
Fair values of each nonvested award (in dollars per share) | $ 74.20 |  |  |

X
- Definition Common Stock Closing Price + References No definition available. + Details
Name: | lnt_CommonStockClosingPrice
Namespace Prefix: | lnt_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Common Stock Closing Price Grant Date + References No definition available. + Details
Name: | lnt_CommonStockClosingPriceGrantDate
Namespace Prefix: | lnt_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Employee Service Share Based Compensation Fair Values Of Each Nonvested Awards + References No definition available. + Details
Name: | lnt_EmployeeServiceShareBasedCompensationFairValuesOfEachNonvestedAwards
Namespace Prefix: | lnt_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated Payout Percentage + References No definition available. + Details
Name: | lnt_EstimatedPayoutPercentage
Namespace Prefix: | lnt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=lnt_PerformanceUnitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardDateAxis=lnt_TwoThousandSixteenGrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardDateAxis=lnt_TwoThousandFifteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardDateAxis=lnt_TwoThousandFourteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |