Increase In Base Rates

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- Definition

Regulatory Matters [Line Items]

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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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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 requested rate increase (decrease) with regulatory agency.

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

+ References

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 405
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Regulatory Matters [Line Items]
Regulatory liabilities		$ 1,537.9			$ 1,497.2
IPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		777.3			755.4
WPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		760.6			741.8
2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Interim rate increase, amount					$ 102.0
Interim rate increase, percent					7.00%
2016 Test Year Retail Electric [Member] \| Alliant Energy and IPL [Member]
Regulatory Matters [Line Items]
Increase in base rates		23.0
Scenario, Forecast [Member] \| 2017 Test Year Retail Gas [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Interim rate increase, amount	$ 11.0
Interim rate increase, percent	5.00%
Subsequent Event [Member] \| 2017 Test Year Retail Gas [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Requested rate increase, amount			$ 20.0
Requested rate increase, percent			8.00%
Subsequent Event [Member] \| 2016 Test Year Retail Electric [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Approved rate increase, amount				$ 130.0
Approved rate increase, percent				9.00%
Revenue Subject to Refund [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		19.0
Revenue Subject to Refund [Member] \| IPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		8.0
Revenue Subject to Refund [Member] \| WPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		$ 11.0