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Electric Capacity Of Wind Project

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Fossil Fueled Energy Generating Units Capacity

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- Definition

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
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- Definition

After tax earnings per share or per unit impact arising from asset impairment.

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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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.

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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.

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

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

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Property, Plant and Equipment (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) MW	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2017 USD ($) MW	Sep. 30, 2016 USD ($)	Dec. 31, 2020 MW	Apr. 30, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction		$ 9.6	$ 15.8	$ 36.7	$ 44.3
Asset valuation charges for Franklin County wind farm, pre-tax		0.0	86.4	0.0	86.4
Asset valuation charge for Franklin County wind farm, after tax			$ 51.0
Asset valuation charges for Franklin County wind farm, after tax (in dollars per share) \| $ / shares			$ 0.23
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction		4.7	$ 13.8	25.1	36.2
Estimated fair value of net assets acquired							$ 32.0
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction		4.9	$ 2.0	$ 11.6	$ 8.1
Marshalltown Generating Station [Member] \| IPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) \| MW				660
Marshalltown Generating Station [Member] \| Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Total project costs		643.0		$ 643.0
Allowance for funds used during construction				$ 81.0
West Riverside Energy Center [Member] \| WPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) \| MW				730
West Riverside Energy Center [Member] \| Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		278.0		$ 278.0
Allowance for funds used during construction				$ 9.0
Expansion of Wind Generation [Member]
Property, Plant and Equipment [Line Items]
Electric capacity of wind farm \| MW				129
Expansion of Wind Generation [Member] \| Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 184.0		$ 184.0
Allowance for funds used during construction				$ 7.0
Scenario, Forecast [Member] \| Expansion of Wind Generation [Member] \| IPL [Member]
Property, Plant and Equipment [Line Items]
Electric capacity of wind farm \| MW						1,000
Scenario, Forecast [Member] \| Expansion of Wind Generation [Member] \| WPL [Member]
Property, Plant and Equipment [Line Items]
Electric capacity of wind farm \| MW	55
Estimated fair value of net assets acquired	$ 74.0