Debt (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended
Apr. 30, 2018	Mar. 31, 2018
Alliant Energy and IPL [Member]
Debt [Line Items]
Commercial paper, long-term		$ 45.9
Commercial paper, long-term, interest rate		2.30%
Term Loan Credit Agreement [Member] \| Subsequent Event [Member] \| Term loan credit agreement through April 2020 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Proceeds from issuance of variable-rate term loan	$ 300.0
Variable-rate term loan, interest rate	2.30%

Contractual interest rate for funds borrowed, under the debt agreement.

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+ References

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19,20,22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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Weighted average interest rate of long-term debt outstanding calculated at point in time.

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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