XML 205 R61.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) (USD $) |  |  |  |  |  |  |  |  | 6 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 30, 2013 Performance Shares [Member] | Dec. 31, 2012 Performance Shares [Member] | Jun. 30, 2012 Performance Shares [Member] | Dec. 31, 2011 Performance Shares [Member] | Jun. 30, 2013 Performance Units [Member] | Dec. 31, 2012 Performance Units [Member] | Jun. 30, 2012 Performance Units [Member] | Dec. 31, 2011 Performance Units [Member] | Jun. 30, 2013 2013 Grant [Member] Performance Shares [Member] | Jun. 30, 2013 2013 Grant [Member] Performance Units [Member] | Jun. 30, 2013 2012 Grant [Member] Performance Shares [Member] | Jun. 30, 2013 2012 Grant [Member] Performance Units [Member] | Jun. 30, 2013 2011 Grant [Member] Performance Shares [Member] | Jun. 30, 2013 2011 Grant [Member] Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nonvested awards (in shares) | 139,940 | [1] | 145,277 | [1] | 145,277 | [1] | 236,979 | [1] | 66,397 | [2] | 64,969 | [2] | 66,804 | [2] | 42,996 | [2] | 49,093 | 22,201 | 45,612 | 23,392 | 45,235 | 20,804
Alliant Energy common stock closing price on June 30, 2013 (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 50.42 |  | $ 50.42 |  | $ 50.42 |
Alliant Energy common stock closing price on grant date (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 47.58 |  | $ 43.05 |  | $ 38.75
Estimated payout percentage based on performance criteria |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 99.00% | 99.00% | 95.00% | 95.00% | 120.00% | 120.00%
Fair values of each nonvested award (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 49.92 | $ 47.10 | $ 47.90 | $ 40.90 | $ 60.50 | $ 46.50
[1] | Share amounts represent the target number of performance shares. Each performance share’s value is based on the price of one share of Alliant Energy’s common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.
[2] | Unit amounts represent the target number of performance units. Each performance unit’s value is based on the closing price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.

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
- 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph b(2)(b) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph b(2)(a) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant