Revenue Recognition - Disaggregation of Revenue (Details) - CAD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,882	$ 1,581	$ 5,264	$ 4,799
Leasing revenues	16	14	46	42
Total revenues	1,898	1,595	5,310	4,841
Freight [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,854	1,547	5,188	4,708
Freight [Member] \| Grain [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	384	351	1,113	1,107
Freight [Member] \| Coal [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	171	165	486	478
Freight [Member] \| Potash [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	130	103	358	310
Freight [Member] \| Fertilizer and Sulphur [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	55	52	171	181
Freight [Member] \| Forest Products [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	76	67	211	202
Freight [Member] \| Energy, Chemicals and Plastic [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	339	208	874	651
Freight [Member] \| Metals, Minerals and Consumer Products [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	208	192	595	552
Freight [Member] \| Automotive [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	85	68	247	223
Freight [Member] \| Intermodal [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	406	341	1,133	1,004
Non-Freight [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 28	$ 34	$ 76	$ 91

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- Definition

The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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