XML 53 R43.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Property, Plant and Equipment (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |  | 3 Months Ended | 9 Months Ended |  | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013 | Dec. 31, 2013 | Sep. 30, 2014 IPL [Member] | Sep. 30, 2013 IPL [Member] | Sep. 30, 2014 IPL [Member] | Sep. 30, 2013 IPL [Member] | Dec. 31, 2013 IPL [Member] | Sep. 30, 2014 George Neal Unit 3 [Member] Alliant Energy and IPL [Member] | Sep. 30, 2014 Ottumwa Unit 1 [Member] Alliant Energy and IPL [Member] | Sep. 30, 2014 Columbia Units 1 and 2 [Member] Alliant Energy and WPL [Member] | Sep. 30, 2014 Edgewater Unit 5 [Member] Alliant Energy and WPL [Member] | Sep. 30, 2014 Marshalltown [Member] MW | Sep. 30, 2014 Marshalltown [Member] Alliant Energy and IPL [Member] | Dec. 31, 2014 Gas distribution assets [Member] Scenario, Forecast [Member] IPL [Member]
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric plant | $ 10,016.3 |  | $ 10,016.3 |  | $ 9,415.7 | $ 5,252.6 |  | $ 5,252.6 |  | $ 5,034.9 | $ 59.0 | $ 151.0 | $ 272.0 | $ 67.0 |  | $ 120.0 |
Allowance for funds used during construction | 8.3 | 8.5 | 25.8 | 21.1 |  | 6.6 | 5.8 | 18.6 | 14.3 |  | 4.0 | 18.0 | 15.0 | 2.0 |  | 2.0 |
Fossil-fueled EGU capacity (in megawatts) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 650 |  |
Expected proceeds from asset sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10

X
- Definition Fossil Fueled Energy Generating Units Capacity + References No definition available. + Details
Name: | lnt_FossilFueledEnergyGeneratingUnitsCapacity
Namespace Prefix: | lnt_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date of long-lived, depreciable electric utility plant. + References No definition available. + Details
Name: | lnt_PublicUtilitiesPropertyPlantAndEquipmentElectric
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total increase in earnings in the period representing the cost of equity (based on assumed rate of return) and/or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments. + References Reference 1: 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=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500269&loc=d3e45485-110386 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44278-110382 + Details
Name: | us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration