Change in Non-Cash Working Capital Balances Related to Operations - Change in Non-Cash Working Capital Balances Related to Operations (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Accounts receivable, net	CAD (91)	CAD 44	CAD 80
Materials and supplies	9	14	15
Other current assets	(26)	(18)	55
Accounts payable and accrued liabilities	(30)	(95)	125
Change in non-cash working capital	CAD (138)	CAD (55)	CAD 275

The increase (decrease) during the reporting period in the amounts payable to vendors for goods and services received and the amount of obligations and expenses incurred but not paid.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Balance Type:	debit
Period Type:	duration

- Definition

The increase (decrease) during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in current assets classified as other.

+ References

No definition available.

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Period Type:	duration

- Definition

The increase (decrease) during the reporting period in the value of raw materials, packaging materials and supplies held in inventory.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of income (expense) included in net income that results in no cash inflow (outflow), classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

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