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Receivables (Receivables Sold Under The Agreement) (Details) (USD $)
In Millions, unless otherwise specified |
Dec. 31, 2012
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Dec. 31, 2011
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| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||||
| Fair value of deferred proceeds | $ 66.8 | $ 53.7 | ||||
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IPL [Member]
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| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||||
| Receivables sold | 198.4 | 195.3 | ||||
| Fair value of deferred proceeds | 66.8 | 53.7 | ||||
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Receivables Sold [Member] | IPL [Member]
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| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||||
| Customer accounts receivable | 118.2 | 122.4 | ||||
| Unbilled utility revenues | 77.4 | 65.4 | ||||
| Other receivables | 2.8 | 7.5 | ||||
| Receivables sold | 198.4 | 195.3 | ||||
| Less: cash proceeds | 130.0 | [1] | 140.0 | [1] | ||
| Deferred proceeds | 68.4 | 55.3 | ||||
| Less: allowance for doubtful accounts | 1.6 | 1.6 | ||||
| Fair value of deferred proceeds | 66.8 | 53.7 | ||||
| Outstanding receivables past due | $ 16.1 | $ 15.9 | ||||
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