v3.5.0.2

Accounting for derivative instruments - gain, loss - (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015
Impact of derivative instruments on the consolidated statements of operations |  |  |  |
Change in fair value of derivative instruments | $ 9.0 | $ 3.6 | $ 20.0 | $ 8.7
Derivative instruments not designated as cash flow hedges |  |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |  |
Change in fair value of derivative instruments | 9.0 | 3.6 | 20.0 | 8.7
Derivative instruments not designated as cash flow hedges | Natural gas swaps |  |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |  |
Realized (gains) and losses of derivative instruments | 0.6 | 1.5 | 4.0 | 4.3
Change in fair value of derivative instruments | 0.2 | (0.1) | 6.0 | 0.7
Derivative instruments not designated as cash flow hedges | Gas purchase agreements |  |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |  |
Realized (gains) and losses of derivative instruments | 12.4 | 11.8 | 36.4 | 36.1
Change in fair value of derivative instruments | 5.6 | 6.1 | 16.8 | 11.6
Derivative instruments not designated as cash flow hedges | Interest rate swaps |  |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |  |
Realized (gains) and losses of derivative instruments | 1.0 | 0.5 | 2.7 | 1.7
Change in fair value of derivative instruments | $ 3.2 | $ (2.4) | $ (2.8) | $ (3.6)

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- Definition The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings. + 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 210.9-04.13(h)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
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