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Receivables (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Long-term debt issued | $ 3,348.4 |  | $ 3,149.9 |  |
Decrease in accounts receivable - other | (49.2) |  | 61.3 |  | (54.3)
IPL [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Receivables sold | 238.0 |  | 198.4 |  |
Long-term debt issued | 1,563.4 |  | 1,363.4 |  |
Decrease in accounts receivable - other | (55.9) |  | (0.7) |  | 22.4
IPL [Member] | Maximum [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Cash proceeds to be received from third-party | 170.0 |  | 160.0 |  | 160.0
IPL [Member] | March 2012 Through March 2014 [Member] | Maximum [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Cash proceeds to be received from third-party | 180.0 |  |  |  |
IPL [Member] | March 2012 Through March 2014 [Member] | Minimum [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Cash proceeds to be received from third-party | 150.0 |  |  |  |
IPL and WPL [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Customer accounts receivable, financing payment term | 5 years |  |  |  |
Franklin County Wind Project [Member] | American Recovery and Reinvestment Act of 2009 [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Reduction to carrying value |  |  | 62 |  |
Decrease in accounts receivable - other | 62.4 |  |  |  |
Senior Debentures [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Long-term debt issued | 1,525.0 |  | 1,275.0 |  |
Senior Debentures [Member] | IPL [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Long-term debt issued | 1,525.0 |  | 1,275.0 |  |
4.7% senior debenture, due 2043 [Member] | Senior Debentures [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Long-term debt issued | 250.0 | [1] | 0 | [1] |
4.7% senior debenture, due 2043 [Member] | Senior Debentures [Member] | IPL [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Long-term debt issued | $ 250.0 | [1] | $ 0 | [1] |
Whiting Petroleum Corporation [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Obligations to pay on tax benefits, percentage | 90.00% |  |  |  |
[1] | In 2013, IPL issued $250.0 million of 4.7% senior debentures due 2043. The proceeds from the issuance were used by IPL to reduce cash proceeds received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt by $65 million and for general working capital purposes.

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- Definition The increase (decrease) during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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