Maximum borrowing capacity that the Company is enabling to issue under the commercial paper program.

No definition available.

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Namespace Prefix:	cni_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items representing amounts of proceeds from and repayments of commercial paper

+ References

No definition available.

+ Details

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- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from borrowing by issuing commercial paper.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3255-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net cash inflow or cash outflow from issuing (borrowing) and repaying commercial paper.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 9
-Subparagraph c
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3098-108585

+ Details

Name:	us-gaap_ProceedsFromRepaymentsOfCommercialPaper
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow due to repaying amounts borrowed by issuing commercial paper.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3291-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_CurrencyAxis=currency_USD
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Long-term debt (Details 2) (Commercial paper) CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 CAD	Dec. 31, 2014 CAD	Dec. 31, 2013 CAD	Dec. 31, 2015 USD ($)
Commercial Paper [Line Items]
Proceeds from Issuance of Commerical Paper	CAD 2,624	CAD 2,443	CAD 3,255
Repayments of Commercial Paper	(2,173)	(2,720)	(2,987)
Net issuance (repayments) Of Commercial Paper	451	(277)	CAD 268
Commercial paper, other disclosues [Abstract]
Debt instrument principal outstanding balance	11,330	9,266
Commercial paper [Member]
Commercial paper, other disclosues [Abstract]
Debt instrument principal outstanding balance	CAD 458	CAD 0
Commercial paper, weighted average interest rate	0.41%			0.41%
Commercial paper maturity	90 days
Commercial paper [Member] \| USD
Commercial paper, other disclosues [Abstract]
Debt instrument principal outstanding balance \| $				$ 331
Commercial paper [Member] \| Maximum [Member]
Commercial paper, other disclosues [Abstract]
Commercial paper, maximum borrowing capacity	CAD 800