Revenue Recognition - Disaggregation of Revenue (Details) - CAD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,734	$ 1,627	$ 3,382	$ 3,218
Total revenues	1,750	1,643	3,412	3,246
Freight [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,709	1,598	3,334	3,161
Freight [Member] \| Grain [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	372	363	729	756
Freight [Member] \| Coal [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	164	165	315	313
Freight [Member] \| Potash [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	116	109	228	207
Freight [Member] \| Fertilizer and Sulphur [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	55	70	116	129
Freight [Member] \| Forest Products [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	69	68	135	135
Freight [Member] \| Energy, Chemicals and Plastic [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	278	216	535	443
Freight [Member] \| Metals, Minerals and Consumer Products [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	204	190	387	360
Freight [Member] \| Automotive [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	91	79	162	155
Freight [Member] \| Intermodal [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	360	338	727	663
Non-Freight [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25	29	48	57
Leasing revenues	$ 16	$ 16	$ 30	$ 28

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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
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-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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