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Debt (Narrative) (Details) - USD ($) | 1 Months Ended | 3 Months Ended
--- | --- | ---
Apr. 30, 2019 | Mar. 31, 2019
Debt [Line Items] |  |
Credit facility agreement, extension |  | 1 year
Line of credit facility, current borrowing capacity |  | $ 1,000,000,000
IPL [Member] |  |
Debt [Line Items] |  |
Line of credit facility, current borrowing capacity |  | 250,000,000
WPL [Member] |  |
Debt [Line Items] |  |
Line of credit facility, current borrowing capacity |  | 300,000,000
Alliant Energy and IPL [Member] |  |
Debt [Line Items] |  |
Commercial paper, long-term |  | $ 115,000,000
Commercial paper, long-term, interest rate percent |  | 2.70%
Senior Debentures [Member] | Subsequent Event [Member] | 3.6% senior debentures due 2029 [Member] | IPL [Member] |  |
Debt [Line Items] |  |
Proceeds from issuance of long-term debt | $ 300,000,000 |
Interest rate, percent | 3.60% |
Parent Company [Member] |  |
Debt [Line Items] |  |
Line of credit facility, current borrowing capacity |  | $ 450,000,000

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + 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 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + 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(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Including the current and noncurrent portions, carrying value as of the balance sheet date of long-term unsecured obligations issued by corporations and other borrowers to investors (with maturities initially 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 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 + Details
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