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Miscellaneous Financial Information - Additional Information (Detail) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Additional Financial Information [Line Items]
Effect of LIFO inventory liquidation on income (loss)	$ (22)	$ 16	$ 5
Difference between LIFO carrying values and replacement cost of inventories	1,200	900
Research and development costs charged to expenses	133	110	$ 111
Accounts payable and accrued liabilities included accrued taxes other than income taxes	$ 397	$ 413

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Additional Financial Information [Line Items]

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Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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The effect of liquidating LIFO (last in first out) inventory layers on income.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
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The excess of replacement or current cost over the stated LIFO (last in first out) inventory value when the LIFO inventory method is utilized.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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