Employee Future Benefits - Summary of Potential Impact on Obligations Arising From Changes in Key Assumptions (Detail) $ in Millions	Dec. 31, 2018 CAD ($)
Actuarial assumption of discount rates [Member] \| Pension defined benefit plans [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Impact of increase in actuarial assumption	$ (423)
Impact of decrease in actuarial assumption	500
Actuarial assumption of discount rates [Member] \| Retiree welfare plans [Member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Impact of increase in actuarial assumption	(62)
Impact of decrease in actuarial assumption	74
Actuarial assumption of medical cost trend rates [Member] \| Retiree welfare plans [Member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Impact of increase in actuarial assumption	21
Impact of decrease in actuarial assumption	(18)
Actuarial assumption of decrease in inflation rates [Member] \| Pension defined benefit plans [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Impact of decrease in actuarial assumption	114
Actuarial assumption of decrease in inflation rates [Member] \| Retiree welfare plans [Member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Impact of decrease in actuarial assumption	$ 14

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

No definition available.

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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by a decrease in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2018-01-01
-Paragraph 145
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_145_a&doctype=Standard
-URIDate 2018-03-16

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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by an increase in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]]

+ References

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