v2.4.0.6

Derivative instruments and hedging activities (Details 5) (Derivative instruments not designated as cash flow hedges, USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2013 | Mar. 31, 2012
Unrealized gains and (losses) |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | $ (12.6) | $ 57.2
Natural gas swaps | Unrealized gains and (losses) |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | (0.4) | 0.9
Gas purchase agreements | Realized (gains) and losses |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | 16.3 | 10.8
Gas purchase agreements | Unrealized gains and (losses) |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | (8.1) | 57.9
Interest rate swaps | Realized (gains) and losses |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | 2.6 | 1.1
Interest rate swaps | Unrealized gains and (losses) |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | (4.1) | (1.6)
Foreign currency forward contracts | Realized (gains) and losses |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | (2.5) | (11.9)
Foreign currency forward contracts | Unrealized gains and (losses) |  |
Impact of derivative instruments on the consolidated statements of operations |  |
Gains and losses for derivative instruments | $ 6.0 | $ 9.2

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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 + Details
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