Revenue Recognition - Disaggregation of Revenue (Details) - CAD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,648	$ 1,591
Total revenues	1,662	1,603
Freight [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,625	1,563
Freight [Member] \| Grain [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	357	393
Freight [Member] \| Coal [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	151	148
Freight [Member] \| Potash [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	112	98
Freight [Member] \| Fertilizer and Sulphur [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	61	59
Freight [Member] \| Forest Products [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	66	67
Freight [Member] \| Energy, Chemicals and Plastic [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	257	227
Freight [Member] \| Metals, Minerals and Consumer Products [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	183	170
Freight [Member] \| Automotive [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	71	76
Freight [Member] \| Intermodal [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	367	325
Non-Freight [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	23	28
Leasing revenues	$ 14	$ 12

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No definition available.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902458&loc=d3e39896-112707

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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