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Receivables (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Feb. 28, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Fair value of deferred proceeds of receivables sold |  | $ 211.1 | $ 172.0 |  |
IPL [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Cash proceeds to be received from third-party |  | 180.0 | 180.0 | $ 180.0 |
Receivables sold to third party |  | 248.1 |  |  |
Fair value of deferred proceeds of receivables sold |  | 211.1 | 172.0 |  |
IPL [Member] | Maximum [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Cash proceeds to be received from third-party |  | 172.0 | 137.0 | 150.0 |
Limit on cash proceeds to be received from third-party |  | 150.0 |  |  |
Whiting Petroleum Corporation [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Final payment of certain future tax benefits expected to be realized |  |  |  | $ 26.0 |
Receivables Sold [Member] | IPL [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Receivables sold to third party |  | 248.1 | 181.1 |  |
Cash proceeds from receivables sold | [1] | 21.0 | 5.0 |  |
Fair value of deferred proceeds of receivables sold |  | $ 211.1 | $ 172.0 |  |
Scenario, Forecast [Member] | IPL [Member] | Maximum [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Limit on cash proceeds to be received from third-party |  |  |  |  | $ 125.0
[1] | Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.

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