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Summary of Interest Expense and Interest Income (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Interest Expense |  |  |  |
Long-Term Debt |  | $ 22.0 | $ 20.5 | $ 20.2
Short-Term Debt |  | 0.9 | 1.1 | 1.2
Regulatory Liabilities |  | 0.9 | 0.6 | 0.6
Interest Expense |  | 23.8 | 22.2 | 22.0
Interest Income |  |  |  |
Interest income |  | (1.9) | (1.3) | (3.2)
Total Interest Expense, net |  | 21.9 | 20.9 | 18.8
Regulatory Assets |  |  |  |
Interest Income |  |  |  |
Interest income |  | (0.7) | (0.6) | (2.3)
AFUDC and Other |  |  |  |
Interest Income |  |  |  |
Interest income | [1] | $ (1.2) | $ (0.7) | $ (0.9)
[1] | AFUDC-Allowance for Funds Used During Construction

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- Definition The amount of interest income and other income recognized during the period. Included in this element is interest derived from investments in debt securities, cash and cash equivalents, and other investments which reflect the time value of money or transactions in which the payments are for the use or forbearance of money and other income from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business). + References No definition available. + Details
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- Definition Amount of the cost of borrowed funds accounted for as interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.9) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition Aggregate amount of interest paid or due on all long-term debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.8) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition The aggregate interest expense incurred on short-term borrowings including commercial paper and Federal funds purchased and securities sold under agreements to repurchase. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.7) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition The net amount of nonoperating interest income (expense). + References No definition available. + Details
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- Definition Regulatory Liability Interest Expense + References No definition available. + Details
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