Fossil Fueled Energy Generating Units Capacity

No definition available.

Name:	lnt_FossilFueledEnergyGeneratingUnitsCapacity
Namespace Prefix:	lnt_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of long-lived, depreciable Alliant Energy Corporate Services, Inc. and other plant.

+ References

No definition available.

+ Details

Name:	lnt_PropertyPlantAndEquipmentNonregulatedBusinessLine2
Namespace Prefix:	lnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated interest costs capitalized as part of property, plant and equipment cost basis.

+ References

No definition available.

+ Details

Name:	us-gaap_AccumulatedCapitalizedInterestCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of gain (loss) from the difference between the sale price or salvage price and the book value of an asset that was sold or retired, and gain (loss) from the write down of assets from their carrying value to fair value.

+ References

No definition available.

+ Details

Name:	us-gaap_GainLossOnSalesOfAssetsAndAssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The increase (decrease) during the reporting period in other noncurrent operating assets not separately disclosed in the statement of cash flows.

+ References

No definition available.

+ Details

Name:	us-gaap_IncreaseDecreaseInOtherNoncurrentAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

+ Details

Name:	us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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_PropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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 980

-SubTopic 340

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44278-110382

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 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

Name:	us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Period end amount of construction work in progress in public utility.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilityAxis=lnt_EdgewaterUnit5Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=lnt_AlliantEnergyAndWplMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilityAxis=lnt_MarshalltownGeneratingStationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=lnt_AlliantEnergyAndIplMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_GasDistributionEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ElectricDistributionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=lnt_CustomerBillingAndInformationSystemMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Property, Plant and Equipment (Narrative) (Details) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2015 USD ($)	Apr. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) MW	Jun. 30, 2014 USD ($)	Dec. 31, 2015 USD ($)
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction			$ 8.6	$ 8.4	$ 15.4	$ 17.5
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction			6.7	$ 6.0	12.0	$ 12.0
Edgewater Unit 5 [Member] \| Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress			132.0		132.0
Allowance for funds used during construction					$ 5.0
Marshalltown [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) \| MW					650
Marshalltown [Member] \| Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress			343.0		$ 343.0
Allowance for funds used during construction					12.0
Gas distribution assets [Member] \| Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Loss on sale of Minnesota distribution assets			3.0		3.0
Gas distribution assets [Member] \| IPL [Member]
Property, Plant and Equipment [Line Items]
Proceeds from asset sales		$ 11.0
Receipt of promissory note		$ 2.0
Electric distribution assets [Member] \| Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Loss on sale of Minnesota distribution assets			9.0		9.0
Customer Billing And Information System [Member]
Property, Plant and Equipment [Line Items]
Capitalized expenditures			79.0		79.0
Capitalized interest			$ 2.0		$ 2.0
Subsequent Event [Member] \| Electric distribution assets [Member] \| IPL [Member]
Property, Plant and Equipment [Line Items]
Proceeds from asset sales	$ 127.0
Scenario, Forecast [Member] \| Electric distribution assets [Member] \| IPL [Member]
Property, Plant and Equipment [Line Items]
Proceeds from asset sales							$ 130.0