Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(h))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

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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

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Accounting for derivative instruments and hedging activities - gain, loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Impact of derivative instruments on the consolidated statements of operations
Change in fair value of derivative instruments	$ (8.9)	$ 2.2	$ 2.1
Derivative instruments not designated as cash flow hedges \| Change in fair value of derivatives
Impact of derivative instruments on the consolidated statements of operations
Unrealized gain (loss) resulting from changes in the fair value of derivative financial instruments	(8.9)	2.2	2.1
Derivative instruments not designated as cash flow hedges \| Natural gas swaps
Impact of derivative instruments on the consolidated statements of operations
Realized loss (gain) for derivative instruments	0.9	0.3	0.4
Derivative instruments not designated as cash flow hedges \| Natural gas swaps \| Change in fair value of derivatives
Impact of derivative instruments on the consolidated statements of operations
Unrealized gain (loss) resulting from changes in the fair value of derivative financial instruments	(4.6)	(0.5)	(1.8)
Derivative instruments not designated as cash flow hedges \| Gas purchase agreements
Impact of derivative instruments on the consolidated statements of operations
Realized loss (gain) for derivative instruments	8.2	4.1	7.5
Derivative instruments not designated as cash flow hedges \| Gas purchase agreements \| Change in fair value of derivatives
Impact of derivative instruments on the consolidated statements of operations
Unrealized gain (loss) resulting from changes in the fair value of derivative financial instruments	3.2	3.7	(5.0)
Derivative instruments not designated as cash flow hedges \| Interest rate swaps
Impact of derivative instruments on the consolidated statements of operations
Realized loss (gain) for derivative instruments	(3.2)	(3.3)	0.9
Derivative instruments not designated as cash flow hedges \| Interest rate swaps \| Change in fair value of derivatives
Impact of derivative instruments on the consolidated statements of operations
Unrealized gain (loss) resulting from changes in the fair value of derivative financial instruments	(7.5)	(1.0)	$ 8.9
Derivative instruments not designated as cash flow hedges \| Convertible Debentures \| Other (income) expense, net
Impact of derivative instruments on the consolidated statements of operations
Unrealized gain (loss) resulting from changes in the fair value of derivative financial instruments	$ 1.8	(1.2)
Derivative instruments not designated as cash flow hedges \| Foreign currency forward contracts \| Foreign exchange loss
Impact of derivative instruments on the consolidated statements of operations
Unrealized gain (loss) resulting from changes in the fair value of derivative financial instruments		$ 0.1