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Gains and Losses on Asset Sales (Parenthetical) (Detail) - CAD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment And Other Income [Line Items]
Gain (loss) on asset sales, before tax	[1]	$ 46	$ 54	$ 220
Gain (loss) on asset sales, after tax	[1]	$ 42	$ 38	192
Surplus Property
Investment And Other Income [Line Items]
Gain (loss) on asset sales, before tax				174
Gain (loss) on asset sales, after tax				$ 151
[1] 2017 included a gain of $174 million ($151 million after tax) from the sale of surplus property in Ontario.

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Investment And Other Income [Line Items]

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Net gain (loss) on asset sales, after tax.

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Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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