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Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Receivables [Line Items] |  |
Customer | $ 92.7 | $ 91.6
Unbilled utility revenues | 68.2 | 82.1
Deferred proceeds | 194.1 | 187.7
Other | 41.5 | 48.0
Allowance for expected credit losses | (10.0) | (7.3)
Accounts receivable, less allowance for expected credit losses | 386.5 | 402.1
IPL [Member] |  |
Receivables [Line Items] |  |
Customer | 0.0 | 0.0
Unbilled utility revenues | 0.0 | 0.0
Deferred proceeds | 194.1 | 187.7
Other | 16.5 | 16.3
Allowance for expected credit losses | (1.7) | (1.2)
Accounts receivable, less allowance for expected credit losses | 208.9 | 202.8
WPL [Member] |  |
Receivables [Line Items] |  |
Customer | 82.4 | 83.5
Unbilled utility revenues | 68.2 | 82.1
Other | 24.5 | 31.4
Allowance for expected credit losses | (8.2) | (6.1)
Accounts receivable, less allowance for expected credit losses | $ 166.9 | $ 190.9

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