Debt (AR Securitization) (Details) - CAD ($)		12 Months Ended
Mar. 20, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Maximum cash proceeds from sale of accounts receivable to unrelated trust		$ 450,000,000
Extension term	1 year
Proceeds		450,000,000	$ 0	$ 0
Repayments		450,000,000	0	$ 0
Outstanding borrowings		$ 0	$ 0

Accounts Receivable Securitization Borrowings

No definition available.

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

- Definition

Accounts Receivable Securitization, Extension Term

+ References

No definition available.

+ Details

Name:	cni_AccountsReceivableSecuritizationExtensionTerm
Namespace Prefix:	cni_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum dollar amount of cash proceeds for undivided co-ownership interest in a revolving pool of accounts receivables company expects in sale.

+ References

No definition available.

+ Details

Name:	cni_SecuritizationProgramMaximumCashProceedsLimit
Namespace Prefix:	cni_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_DebtDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Proceeds from securitizations of receivables treated as collateralized borrowings, which are classified as financing transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-14

+ Details

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

- Definition

Repayments of securitizations of receivables treated as collateralized borrowings, which are classified as financing transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 15
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-15

+ Details

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