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Public Utilities, Refund Received, After Final True-up

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Rate of fuel costs capacity

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Reduction In Fuel-related Costs

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Regulatory Matters [Line Items]

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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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.

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

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

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Percentage of public utility's approved return on equity.

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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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Percentage of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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

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

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

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

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Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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Amount of operating expense for routine plant maintenance, repairs and operations of regulated operation.

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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities			$ 64.8	$ 66.5
Depreciation and amortization	$ 120.7	$ 104.1	342.7	308.7
Regulatory liabilities	628.5		628.5				$ 681.0
Regulatory assets	2,036.5		2,036.5				1,915.1
IPL [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities			49.6	64.5
Other operation and maintenance	104.4	94.8	288.7	279.8
Depreciation and amortization	66.2	52.7	181.0	157.8
Regulatory liabilities	384.8		384.8				430.8
Regulatory assets	1,590.9		1,590.9				1,458.8
WPL [Member]
Regulatory Matters [Line Items]
Other operation and maintenance	66.1	54.2	179.7	157.2
Depreciation and amortization	53.6	$ 48.7	158.8	$ 143.5
Regulatory liabilities	243.7		243.7				250.2
Regulatory assets	445.6		445.6				456.3
2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Write-down of regulatory assets	9.0
2016 Test Year Retail Electric [Member] \| Alliant Energy and IPL [Member]
Regulatory Matters [Line Items]
Increase in base rates	34.0		54.0
2017 and 2018 Test Period Retail Electric [Member] \| Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Increase in base rates	4.0		42.0
2017 and 2018 Test Period Retail Gas [Member] \| Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Increase in base rates	2.0		$ 6.0
2016 Test Year Retail Electric Fuel-related [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Annual bandwidth for fuel-related costs			2.00%
2017 Test Year Retail Electric Fuel-related [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Annual bandwidth for fuel-related costs			2.00%
Scenario, Forecast [Member] \| 2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Requested rate increase (decrease), amount					$ 176.0
Requested rate increase (decrease), percent					12.00%
Interim rate increase (decrease), amount						$ 102.0
Interim rate increase (decrease), percent						7.00%
Settlement agreement rate increase, amount					$ 130.0
Settlement agreement rate increase, percent					9.00%
Scenario, Forecast [Member] \| 2017 and 2018 Test Period Retail Electric [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Increase in base rates						$ 60.0
Authorized increase (decrease) in final rates, amount						$ 9.0
Authorized increase (decrease) in final rates, percent						1.00%
Reduction in fuel-related costs						$ 51.0
Scenario, Forecast [Member] \| 2017 and 2018 Test Period Retail Gas [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount						$ 9.0
Authorized increase (decrease) in final rates, percent						13.00%
Scenario, Forecast [Member] \| 2018 Test Year Retail Electric Fuel-related [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Requested rate increase (decrease), amount					$ 6.0
Requested rate increase (decrease), percent					1.00%
FERC [Member] \| MISO Transmission Owner Complaints [Member]
Regulatory Matters [Line Items]
Base return on equity for refund period from November 12, 2013 through February 11, 2015, percent			10.32%
Refund received, after final true-up			$ 50.0
FERC [Member] \| MISO Transmission Owner Complaints [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Refund received, after final true-up			39.0
FERC [Member] \| MISO Transmission Owner Complaints [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Refund received, after final true-up			11.0
Asset retirement obligations [Member]
Regulatory Matters [Line Items]
Regulatory assets	107.9		107.9				105.9
Asset retirement obligations [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	71.9		71.9				64.3
Asset retirement obligations [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	36.0		36.0				41.6
Asset retirement obligations [Member] \| 2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Depreciation and amortization	5.0
Asset retirement obligations [Member] \| IUB [Member] \| Scenario, Forecast [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Requested recovery period					4 years
Other [Member]
Regulatory Matters [Line Items]
Regulatory assets	90.0		90.0				76.6
Other [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	51.0		51.0				41.9
Other [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	39.0		39.0				34.7
Other [Member] \| 2017 Test Year Retail Electric Fuel-related [Member] \| Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	3.0		3.0
IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	45.0		45.0				83.5
IPL's tax benefit riders [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	45.0		45.0				83.5
IPL's tax benefit riders [Member] \| Alliant Energy and IPL [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities			17.0
Commodity cost recovery [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	21.2		21.2				30.8
Commodity cost recovery [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	15.0		15.0				17.8
Commodity cost recovery [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	6.2		6.2				$ 13.0
Commodity cost recovery [Member] \| 2016 Test Year Retail Electric Fuel-related [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities	3.0		3.0
Commodity cost recovery [Member] \| 2017 Test Year Retail Electric Fuel-related [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	6.0		$ 6.0
Sutherland Units 1 And 3 [Member] \| 2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Other operation and maintenance	$ 4.0
Sutherland Units 1 And 3 [Member] \| IUB [Member] \| Scenario, Forecast [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Requested recovery period					10 years
Sutherland Units 1 And 3 [Member] \| FERC [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Requested recovery period			10 years