Fossil Fueled Energy Generating Units Capacity

No definition available.

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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

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- 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.

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- 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=66902209&loc=d3e3602-108585

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- Definition

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

+ References

No definition available.

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- Definition

Period end book value of other property, plant and equipment (PPE) owned (but not classified elsewhere) by the public utility.

+ References

No definition available.

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Property, Plant and Equipment (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) MW	Mar. 31, 2016 USD ($)	Apr. 30, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 17.0	$ 13.2
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	14.3	10.3
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 2.7	$ 2.9
Marshalltown [Member] \| IPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) \| MW	660
Marshalltown [Member] \| Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Capitalized expenditures	$ 635.0
Allowance for funds used during construction	$ 79.0
Riverside Energy Center Expansion [Member] \| WPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) \| MW	730
Riverside Energy Center Expansion [Member] \| Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 3.0
Construction work in progress	$ 129.0
Subsequent Event [Member] \| Franklin County Wind Farm [Member]
Property, Plant and Equipment [Line Items]
Value of Franklin County wind farm			$ 33.0