v2.4.0.8

Derivative instruments and hedging activities (Tables)

9 Months Ended

Sep. 30, 2013

Derivative instruments and hedging activities

Schedule of notional volumes of forecasted transactions

		Units		September 30, 2013			December 31, 2012
Natural gas swaps		Natural Gas (Mmbtu)			5.6			10.6
Gas purchase agreements		Natural Gas (GJ)			43.9			49.8
Interest rate swaps		Interest (US$)			164.4			172.0
Foreign currency forwards		Cdn$			34.9			176.6

Schedule of fair value of derivative instruments

		September 30, 2013
		Derivative Assets			Derivative Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current		$	—		$	1.3
Interest rate swaps long-term			—			3.2
Total derivative instruments designated as cash flow hedges			—			4.5
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current			—			7.5
Interest rate swaps long-term			7.9			12.6
Foreign currency forward contracts current			0.6			0.3
Foreign currency forward contracts long-term			1.6			—
Natural gas swaps current			—			1.2
Natural gas swaps long-term			—			3.9
Gas purchase agreements current			—			22.8
Gas purchase agreements long-term			—			67.4
Total derivative instruments not designated as cash flow hedges			10.1			115.7
Total derivative instruments		$	10.1		$	120.2

		December 31, 2012
		Derivative Assets			Derivative Liabilities
Derivative instruments designated as cash flow hedges:
Interest rate swaps current		$	—		$	1.3
Interest rate swaps long-term			—			5.2
Total derivative instruments designated as cash flow hedges			—			6.5
Derivative instruments not designated as cash flow hedges:
Interest rate swaps current			—			7.3
Interest rate swaps long-term			0.1			27.7
Foreign currency forward contracts current			9.5			—
Foreign currency forward contracts long-term			11.0			—
Natural gas swaps current			—			—
Natural gas swaps long-term			0.1			3.9
Gas purchase agreements current			0.1			24.5
Gas purchase agreements long-term			—			81.4
Total derivative instruments not designated as cash flow hedges			20.8			144.8
Total derivative instruments		$	20.8		$	151.3

Schedule of changes in OCI attributable to derivative financial instruments

(in millions) Three months ended September 30, 2013		Interest Rate Swaps			Natural Gas Swaps			Total
Accumulated OCI balance at June 30, 2013		$	(0.4	)	$	—		$	(0.4	)
Change in fair value of cash flow hedges			(0.1	)		—			(0.1	)
Realized from OCI during the period			0.2			—			0.2
Accumulated OCI balance at September 30, 2013		$	(0.3	)	$	—		$	(0.3	)

(in millions) Three months ended September 30, 2012		Interest Rate Swaps			Natural Gas Swaps			Total
Accumulated OCI balance at June 30, 2012		$	(1.7	)	$	0.2		$	(1.5	)
Change in fair value of cash flow hedges			(0.3	)		—			(0.3	)
Realized from OCI during the period			0.2			(0.1	)		0.1
Accumulated OCI balance at September 30, 2012		$	(1.8	)	$	0.1		$	(1.7	)

(in millions) Nine months ended September 30, 2013		Interest Rate Swaps			Natural Gas Swaps			Total
Accumulated OCI balance at December 31, 2012		$	(1.5	)	$	0.1		$	(1.4	)
Change in fair value of cash flow hedges			0.5			—			0.5
Realized from OCI during the period			0.7			(0.1	)		0.6
Accumulated OCI balance at September 30, 2013		$	(0.3	)	$	—		$	(0.3	)

(in millions) Nine months ended September 30, 2012		Interest Rate Swaps			Natural Gas Swaps			Total
Accumulated OCI balance at December 31, 2011		$	(1.7	)	$	0.3		$	(1.4	)
Change in fair value of cash flow hedges			(0.8	)		—			(0.8	)
Realized from OCI during the period			0.7			(0.2	)		0.5
Accumulated OCI balance at September 30, 2012		$	(1.8	)	$	0.1		$	(1.7	)

Summary of realized (gains) and losses for derivative instruments not designated as cash flow hedges

				Three months ended September 30,
		Classification of (gain) loss recognized in income
				2013			2012
Gas purchase agreements		Fuel		$	7.6		$	13.3
Foreign currency forwards		Foreign exchange gain			(1.1	)		(2.1	)
Interest rate swaps		Interest, net			2.7			1.2

				Nine months ended September 30,
		Classification of (gain) loss recognized in income
				2013			2012
Gas purchase agreements		Fuel		$	38.0		$	29.3
Foreign currency forwards		Foreign exchange gain			(14.4	)		(17.3	)
Interest rate swaps		Interest, net			9.4			3.4

Summary of the unrealized gains and losses resulting from changes in the fair value of derivative financial instruments that are not designated as cash flow hedges

				Three months ended September 30,
		Classification of (gain) loss recognized in income
				2013			2012
Natural gas swaps		Change in fair value of derivatives		$	0.6		$	(1.0	)
Gas purchase agreements		Change in fair value of derivatives			3.6			(10.0	)
Interest rate swaps		Change in fair value of derivatives			(0.7	)		0.3
Total change in fair value of derivative instruments				$	3.5		$	(10.7	)
Foreign currency forwards		Foreign exchange loss (gain)		$	(0.2	)	$	(4.7	)

				Nine months ended September 30,
		Classification of (gain) loss recognized in income
				2013			2012
Natural gas swaps		Change in fair value of derivatives		$	1.4		$	(0.2	)
Gas purchase agreements		Change in fair value of derivatives			(12.0	)		(49.3	)
Interest rate swaps		Change in fair value of derivatives			(22.8	)		(1.8	)
Total change in fair value of derivative instruments				$	(33.4	)	$	(51.3	)
Foreign currency forwards		Foreign exchange loss (gain)		$	18.5		$	8.2

X

- Definition

Tabular disclosure for realized gains and losses on derivative instruments not designated as hedging instruments of (a) the location and amount of gains and losses reported in the statement of financial performance and (b) the location and fair value amounts of the instruments reported in the statement of financial position.

+ References

No definition available.

+ Details

Name:	at_ScheduleOfGainLossOnSaleOfDerivativesNotDesignatedAsHedgingInstrumentsStatementsOfFinancialPerformanceAndFinancialPositionLocationTableTextBlock
Namespace Prefix:	at_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure for unrealized gains and losses on derivative instruments not designated as hedging instruments of (a) the location and amount of gains and losses reported in the statement of financial performance and (b) the location and fair value amounts of the instruments reported in the statement of financial position.

+ References

No definition available.

+ Details

Name:	at_ScheduleOfUnrealizedGainLossOnDerivativesNotDesignatedAsHedgingInstrumentsStatementsOfFinancialPerformanceAndFinancialPositionLocationTableTextBlock
Namespace Prefix:	at_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of the effective portion of the gains and losses on derivative instruments designated (and non-derivative instruments) designated and qualifying in cash flow hedges and net investment hedges that was recognized in other comprehensive income (loss) during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

+ Details

Name:	us-gaap_ScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of the location and fair value amounts of derivative instruments (and nonderivative instruments that are designated and qualify as hedging instruments) reported in the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

+ Details

Name:	us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of the notional amounts of outstanding derivative positions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959

+ Details

Name:	us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration