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Receivables (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended |  |  | 1 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2013 | Sep. 30, 2012 | Sep. 30, 2013 IPL [Member] | Dec. 31, 2012 IPL [Member] | Oct. 31, 2013 Senior Debentures [Member] 4.7% senior debentures [Domain] Subsequent Event [Member] IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Receivables sold |  |  | $ 229.8 | $ 198.4 |
Proceeds from issuance of long-term debt | 0 | 75.0 |  |  | 250.0
Proceeds from Franklin County wind project cash grant | $ 62.4 | $ 0 |  |  |

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