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.

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

Derivatives (Narrative) (Details) - Derivatives designated as hedging instruments: gal in Millions, CAD in Millions		3 Months Ended	9 Months Ended
	Sep. 30, 2017 gal	Sep. 30, 2017 CAD	Sep. 30, 2017 CAD
Eliminations \| Foreign currency forward contracts
Derivative [Line Items]
Derivative purchases of underlying currency (in Canadian Dollars) \| CAD		CAD 326	CAD 728
Cash flow hedging \| Fixed price diesel swaps
Derivative [Line Items]
Fixed price swap contract (in gallons) \| gal	2.7