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Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Customer | $ 111.7 | $ 93.8
Unbilled utility revenues | 90.2 | 83.1
Deferred proceeds | 211.1 | 172.0
Other | 89.0 | 53.5
Allowance for doubtful accounts | (8.7) | (4.8)
Accounts receivable, less allowance for doubtful accounts | 493.3 | 397.6
IPL [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Customer | 0.0 | 4.6
Unbilled utility revenues | 0.0 | 1.2
Deferred proceeds | 211.1 | 172.0
Other | 30.7 | 22.8
Allowance for doubtful accounts | (1.1) | (0.6)
Accounts receivable, less allowance for doubtful accounts | 240.7 | 200.0
WPL [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Customer | 104.4 | 81.5
Unbilled utility revenues | 90.2 | 81.9
Other | 38.8 | 25.7
Allowance for doubtful accounts | (7.1) | (3.7)
Accounts receivable, less allowance for doubtful accounts | $ 226.3 | $ 185.4

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- Definition Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business. + 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(3)) -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 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(5)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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