Pension and Other Benefits - Narrative (Details) - Pension Plans, Defined Benefit [Member] - CAD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Contributions made by the company	$ 12	$ 11	$ 23	$ 12
Refund of plan surplus				$ 10

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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