Accounting for derivative instruments and hedging activities (Tables)

6 Months Ended

Jun. 30, 2016

Accounting for derivative instruments and hedging activities

Schedule of notional volumes of forecasted transactions

		June 30,	December 31,
	Units	2016	2015
Natural gas swaps	Natural Gas (Mmbtu)	5.7	2.8
Gas purchase agreements	Natural Gas (Gigajoules)	19.4	25.0
Interest rate swaps	Interest (US$)	532.3	302.3

Schedule of fair value of derivative instruments

	June 30, 2016
	Derivative		Derivative
	Assets		Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current	$	—	$	1.0
Interest rate swaps long-term		—		3.2
Total derivative instruments designated as cash flow hedges		—		4.2
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current		—		3.3
Interest rate swaps long-term		—		12.4
Natural gas swaps current		1.6		1.9
Natural gas swaps long-term		1.1		—
Gas purchase agreements current		—		17.4
Gas purchase agreements long-term		—		12.9
Total derivative instruments not designated as cash flow hedges		2.7		47.9
Total derivative instruments	$	2.7	$	52.1

	December 31, 2015
	Derivative		Derivative
	Assets		Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current	$	—	$	1.0
Interest rate swaps long-term		—		2.7
Total derivative instruments designated as cash flow hedges		—		3.7
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current		—		2.0
Interest rate swaps long-term		0.3		7.8
Natural gas swaps current		—		5.0
Natural gas swaps long-term		—		—
Gas purchase agreements current		—		28.7
Gas purchase agreements long-term		—		10.3
Total derivative instruments not designated as cash flow hedges		0.3		53.8
Total derivative instruments	$	0.3	$	57.5

Schedule of changes in OCI attributable to derivative financial instruments

	Interest Rate
Three Months Ended June 30, 2016	Swaps
Accumulated OCI balance at March 31, 2016	$	(0.1)
Change in fair value of cash flow hedges		(0.2)
Realized from OCI during the period		0.2
Accumulated OCI balance at June 30, 2016	$	(0.1)
	Interest Rate
Three Months Ended June 30, 2015	Swaps
Accumulated OCI balance at March 31, 2015	$	(0.2)
Change in fair value of cash flow hedges		0.2
Realized from OCI during the period		0.1
Accumulated OCI balance at June 30, 2015	$	0.1
	Interest Rate
Six Months Ended June 30, 2016	Swaps
Accumulated OCI balance at January 1, 2016	$	0.2
Change in fair value of cash flow hedges		(0.7)
Realized from OCI during the period		0.4
Accumulated OCI balance at June 30, 2016	$	(0.1)
	Interest Rate
Six Months Ended June 30, 2015	Swaps
Accumulated OCI balance at January 1, 2015	$	0.1
Change in fair value of cash flow hedges		(0.4)
Realized from OCI during the period		0.4
Accumulated OCI balance at June 30, 2015	$	0.1

Summary of realized loss (gain) for derivative instruments not designated as cash flow hedges

	Classification of loss (gain)	Three Months Ended June 30,				Six Months Ended June 30,
	recognized in income	2016		2015		2016		2015
Gas purchase agreements	Fuel	$	12.5	$	12.3		24.0	$	24.2
Natural gas swaps	Fuel		1.3		1.6		3.3		3.0
Interest rate swaps	Interest, net		1.1		1.0		1.7		1.9

Summary of the unrealized loss (gain) resulting from changes in the fair value of derivative financial instruments that are not designated as cash flow hedges

	Classification of gain (loss)	Three Months Ended June 30,				Six Months Ended June 30,
	recognized in income	2016		2015		2016		2015
Natural gas swaps	Change in fair value of derivatives	$	4.0	$	1.4	$	5.8	$	0.8
Gas purchase agreements	Change in fair value of derivatives		11.4		3.9		11.2		5.6
Interest rate swaps	Change in fair value of derivatives		(3.2)		1.5		(6.0)		(1.2)
		$	12.2	$	6.8	$	11.0	$	5.2