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

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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3255-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

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The cash outflow due to repaying amounts borrowed by issuing commercial paper.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
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Debt (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended		9 Months Ended
Debt (Narrative) (Details) - USD ($) $ in Millions	Oct. 31, 2016	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Debt [Line Items]
Long-term debt issued			$ 300.0	$ 250.7
IPL [Member]
Debt [Line Items]
Long-term debt issued			300.0	$ 250.0
Repayments of commercial paper			$ 100.0
Senior Debentures [Member] \| 3.7% senior debenture, due 2046 [Member] \| IPL [Member]
Debt [Line Items]
Long-term debt issued		$ 300.0
Interest rate		3.70%	3.70%
Subsequent Event [Member] \| Term Loan Credit Agreement [Member] \| Term Loan Credit Agreement Through 2018, 1% at September 30, 2016 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt issued	$ 500.0
Interest rate	1.30%