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Regulatory Matters (Tax Benefit Riders) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Regulatory Liabilities [Line Items]
Decrease in regulatory liabilities	$ (19.0)	$ (29.2)
Alliant Energy and IPL [Member] | Electric tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Decrease in regulatory liabilities	(33.0)
Alliant Energy and IPL [Member] | Gas tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Decrease in regulatory liabilities	(3.0)
Alliant Energy and IPL [Member] | Tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Decrease in regulatory liabilities	$ (36.0)

X

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

+ Details

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Balance Type:	debit
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X

- 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.

+ Details

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- Details

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X

- Details

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- Details

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X

- Details

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