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Public Utilities, Requested Rate Increase (Decrease), Simple Average of Actual Costs Incurred During Test Year, Simple Average Basis

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Rate of fuel costs capacity

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Regulatory Matters [Line Items]

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Under Collection Of Retail Fuel Related Costs

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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Revenue derived from the regulated (by a federal, state, or local government or agency) generation, transmission and distribution of electricity.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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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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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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-Name Accounting Standards Codification
-Topic 980
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Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base.

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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended				36 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2016
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		$ (67.8)	$ 10.8	$ (90.8)
Electric revenues		2,770.5	2,713.6	2,689.0
Regulatory liabilities		737.7	821.2
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return		$ 30.0
Period for simple average of actual costs incurred during Test Year		2 years
Increase (decrease) in regulatory liabilities		$ (75.5)	(18.9)	(82.3)
Electric revenues		1,503.8	1,493.3	1,491.8
Regulatory liabilities		489.2	583.5
Billing credits to reduce retail electric customers' bills		24.0	72.0
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return		$ 12.0
Expenditure collection period after new rate implementation		5 years
Increase (decrease) in regulatory liabilities		$ 7.7	29.7	(8.5)
Electric revenues		1,266.7	1,220.3	1,197.2
Regulatory liabilities		248.5	237.7
WPL [Member] \| 2013/2014 Test Period Retail Electric And Gas Final Order [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount			(13.0)
Alliant Energy and IPL [Member] \| Revenue Requirement Adjustment [Member]
Regulatory Matters [Line Items]
Electric revenues		14.0	15.0	24.0
Alliant Energy and WPL [Member] \| Deferral [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		8.0
Scenario, Forecast [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Billing credits to reduce retail electric customers' bills	$ 9.0				$ 105.0
Scenario, Forecast [Member] \| Alliant Energy and IPL [Member] \| Revenue Requirement Adjustment [Member]
Regulatory Matters [Line Items]
Electric revenues	15.0
Electric [Member] \| Alliant Energy and IPL [Member] \| IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		(72.0)	(85.0)	(79.0)
Electric [Member] \| Scenario, Forecast [Member] \| Alliant Energy and IPL [Member] \| IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities	(65.0)
Gas [Member] \| IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		(12.0)
Gas [Member] \| Alliant Energy and IPL [Member] \| IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		$ (12.0)	(12.0)	$ (11.0)
Nelson Dewey Units 1 and 2 and Edgewater Unit Three [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Expenditure collection period after new rate implementation		10 years
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]
Retail electric fuel-related costs		$ 28.0	28.0
Under-collection of retail fuel related costs			33.0
2015/2016 Test Period Retail Electric And Gas [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		(5.0)
2016 Test Year Retail Electric Fuel Related [Member] \| Scenario, Forecast [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount	$ 7.0
Authorized increase (decrease) in final rates, percent	1.00%
Annual bandwidth for fuel-related costs	2.00%
2015 Test Year Retail Electric Fuel Related [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		$ 39.0
Authorized increase (decrease) in final rates, percent		4.00%
Annual bandwidth for fuel-related costs		2.00%
2015 Test Year Retail Electric Fuel Related [Member] \| Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Over-collection of retail fuel-related costs			$ 10.0
Fuel [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Retail electric fuel-related costs		$ 25.0
Sales [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Retail electric fuel-related costs		$ 14.0