Overcollection Of Retail Fuel Related Costs

No definition available.

Name:	lnt_OverCollectionOfRetailFuelRelatedCosts
Namespace Prefix:	lnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Rate of fuel costs capacity

+ References

No definition available.

+ Details

Name:	lnt_RateOfFuelCostsCapacity
Namespace Prefix:	lnt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Regulatory Matters [Line Items]

+ References

No definition available.

+ Details

Name:	lnt_RegulatoryMattersLineItems
Namespace Prefix:	lnt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of capitalized fuel costs of a regulated entity that are expected to be recoverable through rate adjustments within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499739&loc=d3e43603-110378

+ Details

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

- Definition

The increase (decrease) during the reporting period in regulated liabilities. Regulated liabilities are created when regulatory agency permits an entity to defer revenues to the balance sheet.

+ 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 (a)

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

+ Details

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

- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

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

- Definition

Percentage of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

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

- Definition

Percentage of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=lnt_TaxBenefitRiderMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=lnt_TwoThousandFourteenTestYearRetailElectricFuelRelatedRequestMember
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_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=lnt_TwoThousandSixteenTestYearRetailElectricFuelRelatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2016	Dec. 31, 2014
Regulatory Matters [Line Items]
Decrease in regulatory liabilities	$ (40.0)	$ 45.2
Alliant Energy and IPL [Member] \| Tax benefit riders [Member]
Regulatory Matters [Line Items]
Decrease in regulatory liabilities	41.0
WPL [Member]
Regulatory Matters [Line Items]
Decrease in regulatory liabilities	(1.1)	$ 47.9
2014 Test Year Retail Electric Fuel Related [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Annual bandwidth for fuel-related costs				2.00%
2014 Test Year Retail Electric Fuel Related [Member] \| Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Under-collection of retail fuel-related costs				$ 33.0
Fuel-related costs	$ 28.0
Subsequent Event [Member] \| 2016 Test Year Retail Electric Fuel Related [Member]
Regulatory Matters [Line Items]
Requested rate increase (decrease), amount			$ 15.0
Requested rate increase (decrease), percentage			1.00%
Subsequent Event [Member] \| 2014 Test Year Retail Electric Fuel Related [Member]
Regulatory Matters [Line Items]
Approved rate increase (decrease), amount			$ 28.0
Approved rate increase (decrease), percentage			3.00%