XML 47 R47.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2013 wind_projects | Mar. 31, 2012
Income Tax [Line Items] |  |
Statutory federal income tax rate | 35.00% |
Income tax rates for continuing operations | 12.70% | 39.00%
Wind projects generating production tax credits (in wind projects) | 3 |
Increase (decrease) non-current deferred tax liabilities | $ (32.8) |
State Apportionment [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations |  | 21.40%
Deferred income tax expense |  | 15
Tax Benefit Rider [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations | 12.80% | 12.20%
Rate-making On Property-related Differences [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations | 5.00% | 1.70%
Deferred income tax assets [Member] |  |
Income Tax [Line Items] |  |
Increase (decrease) current deferred tax assets | (77.7) |
IPL [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations | (24.00%) | 125.40%
Increase (decrease) non-current deferred tax liabilities | (7.7) |
IPL [Member] | State Apportionment [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations |  | 137.30%
Deferred income tax expense |  | 8
IPL [Member] | Tax Benefit Rider [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations | 37.30% | 37.50%
IPL [Member] | Rate-making On Property-related Differences [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations | 14.00% | 2.10%
IPL [Member] | Whispering Willow - East Wind Project [Member] |  |
Income Tax [Line Items] |  |
Electric capacity of wind projects generating production tax credits (in megawatts) | 200 |
IPL [Member] | Deferred income tax assets [Member] |  |
Income Tax [Line Items] |  |
Increase (decrease) current deferred tax assets | (20.6) |
WPL [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations | 32.00% | 44.10%
Increase (decrease) non-current deferred tax liabilities | (32.9) |
WPL [Member] | State Apportionment [Member] |  |
Income Tax [Line Items] |  |
Income tax rates for continuing operations |  | 12.30%
Deferred income tax expense |  | 7
WPL [Member] | Cedar Ridge Wind Project [Member] |  |
Income Tax [Line Items] |  |
Electric capacity of wind projects generating production tax credits (in megawatts) | 68 |
WPL [Member] | Bent Tree - Phase I Wind Project [Member] |  |
Income Tax [Line Items] |  |
Electric capacity of wind projects generating production tax credits (in megawatts) | 200 |
WPL [Member] | Deferred income tax assets [Member] |  |
Income Tax [Line Items] |  |
Increase (decrease) current deferred tax assets | $ (63.0) |

X
- Definition Electric Capacity Of Wind Project + References No definition available. + Details
Name: | lnt_ElectricCapacityOfWindProject
Namespace Prefix: | lnt_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | lnt_IncomeTaxLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Increase Decrease In Deferred Income Taxes Noncurrent Liabilities + References No definition available. + Details
Name: | lnt_IncreaseDecreaseInDeferredIncomeTaxesNoncurrentLiabilities
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of wind projects generating production tax credits + References No definition available. + Details
Name: | lnt_WindProjectsGeneratingProductionTaxCredits
Namespace Prefix: | lnt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The component of income tax expense for the period representing the increase (decrease) in the entity's deferred tax assets and liabilities pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 289 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 45 -Subparagraph 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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I.7) -URI http://asc.fasb.org/extlink&oid=6889476&loc=d3e330036-122817 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Deferred Tax Expense (or Benefit) -URI http://asc.fasb.org/extlink&oid=6510177 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690 Reference 10: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section I -Subsection 7 + Details
Name: | us-gaap_DeferredIncomeTaxExpenseBenefit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Subparagraph 2 -Article 4 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 47 -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 Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(2)) -URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690 + Details
Name: | us-gaap_EffectiveIncomeTaxRateContinuingOperations
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 47 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=6889476&loc=d3e330036-122817 + Details
Name: | us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in the account that represents the temporary difference that results from Income or Loss that is recognized for accounting purposes but not for tax purposes and vice versa. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration