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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Debt (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended
Debt (Narrative) (Details) - USD ($) $ in Millions	Oct. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Apr. 30, 2018
Term Loan Credit Agreement [Member] \| Short-term loan credit agreement through 2018 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Retirement of debt			$ 95
Term Loan Credit Agreement [Member] \| Term loan credit agreement through April 2020 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt				$ 300
Interest rate, percent		2.80%
Term Loan Credit Agreement [Member] \| Term loan credit agreement through 2018 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Retirement of debt			500
Senior Notes [Member] \| 3.75% senior notes due 2023 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt			400
Interest rate, percent		3.75%
Senior Notes [Member] \| 4.25% senior notes due 2028 [Member] \| Alliant Energy Finance LLC [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt			$ 300
Interest rate, percent		4.25%
Senior Debentures [Member] \| 4.1% senior debentures due 2028 [Member] \| IPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt		$ 500
Interest rate, percent		4.10%
Senior Debentures [Member] \| 5.875% senior debentures due 2018 [Member] \| IPL [Member]
Debt [Line Items]
Retirement of debt		$ 100
Interest rate, percent		5.875%
Senior Debentures [Member] \| 7.25% senior debentures due 2018 [Member] \| IPL [Member]
Debt [Line Items]
Interest rate, percent		7.25%
Senior Debentures [Member] \| Subsequent Event [Member] \| 7.25% senior debentures due 2018 [Member] \| IPL [Member]
Debt [Line Items]
Retirement of debt	$ 250