v2.4.0.8

Derivative instruments and hedging activities (Details 2) In Millions, unless otherwise specified | Sep. 30, 2013 Natural gas swaps MMBTU | Dec. 31, 2012 Natural gas swaps MMBTU | Sep. 30, 2013 Gas purchase agreements gigajoule | Dec. 31, 2012 Gas purchase agreements gigajoule | Sep. 30, 2013 Interest rate swaps USD ($) | Dec. 31, 2012 Interest rate swaps USD ($) | Sep. 30, 2013 Foreign currency forwards CAD | Dec. 31, 2012 Foreign currency forwards CAD
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Derivative instruments |  |  |  |  |  |  |  |
Volume of forecasted transactions | 5,600,000 | 10,600,000 | 43,900,000 | 49,800,000 |  |  |  |
Volume of forecasted transactions, (in dollars) |  |  |  |  | $ 164.4 | $ 172.0 | 34.9 | 176.6

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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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