Financial instruments	12 Months Ended
Dec. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial instruments	Financial instruments A. Fair values of financial instruments The Company categorizes its financial assets and liabilities measured at fair value into a three-level hierarchy that prioritizes those inputs to valuation techniques used to measure fair value based on the degree to which they are observable. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices in active markets for identical assets and liabilities; Level 2 inputs, other than quoted prices included within Level 1, are observable for the asset or liability either directly or indirectly; and Level 3 inputs are not observable in the market. The Company’s short-term financial instruments include cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities, and short-term borrowings including commercial paper and term loans. The carrying value of short-term financial instruments approximate their fair values. The carrying value of the Company’s debt does not approximate its fair value. The estimated fair value has been determined based on market information where available, or by discounting future payments of principal and interest at estimated interest rates expected to be available to the Company at period end. All measurements are classified as Level 2. The Company’s long-term debt, including current maturities, with a carrying value of $20,749 million as at December 31, 2024 (December 31, 2023 - $21,437 million), had a fair value of $18,911 million (December 31, 2023 - $20,550 million). B. Financial risk management Derivative financial instruments Derivative financial instruments may be used to selectively reduce volatility associated with fluctuations in interest rates, FX rates, the price of fuel, and stock-based compensation expense. Where derivatives are designated as hedging instruments, the relationship between the hedging instruments and their associated hedged items is documented, as well as the risk management objective and strategy for the use of the hedging instruments. This documentation includes linking the derivatives that are designated as fair value or cash flow hedges to specific assets or liabilities on the Company's Consolidated Balance Sheets, commitments, or forecasted transactions. At the time a derivative contract is entered into and at least quarterly thereafter, an assessment is made as to whether the derivative item is effective in offsetting the changes in fair value or cash flows of the hedged items. The derivative qualifies for hedge accounting treatment if it is effective in substantially mitigating the risk it was designed to address. It is not the Company’s intent to use financial derivatives or commodity instruments for trading or speculative purposes. Credit risk management Credit risk refers to the possibility that a customer or counterparty will fail to fulfil its obligations under a contract and as a result create a financial loss for the Company. The railway industry predominantly serves financially established customers, and the Company has experienced limited financial losses with respect to credit risk. The credit worthiness of customers is assessed using credit scores supplied by a third party and through direct monitoring of their financial well-being on a continual basis. The Company establishes guidelines for customer credit limits and should thresholds in these areas be reached, appropriate precautions are taken to improve collectability. Counterparties to financial instruments expose the Company to credit losses in the event of non-performance. Counterparties for derivative and cash transactions are limited to high credit quality financial institutions, which are monitored on an ongoing basis. Counterparty credit assessments are based on the financial health of the institutions and their credit ratings from external agencies. The Company does not anticipate non-performance that would materially impact the Company’s Consolidated Financial Statements. In addition, the Company believes there are no significant concentrations of credit risk. FX management The Company conducts business transactions and owns assets in Canada, the U.S., and Mexico. As a result, the Company is exposed to fluctuations in the value of financial commitments, assets, liabilities, income, or cash flows due to changes in FX rates. The Company may enter into FX risk management transactions primarily to manage fluctuations in the exchange rate between Canadian and U.S. currencies, along with fluctuations in the Mexican peso and U.S dollar as discussed below in "Foreign currency derivative instruments". FX exposure is primarily mitigated through natural offsets created by revenues, expenditures, and balance sheet positions incurred in the same currency. Where appropriate, the Company may negotiate with customers and suppliers to reduce the net exposure. Net investment hedge The majority of the Company’s U.S. dollar-denominated long-term debt, finance lease obligations, and operating lease liabilities have been designated as a hedge of the Company's net investment in foreign subsidiaries. This designation has the effect of mitigating volatility on Net income by offsetting long-term FX gains and losses on U.S. dollar-denominated long-term debt and gains and losses on its net investment. The effect of the Company's net investment hedge recognized in “Other comprehensive income (loss)” in 2024 was an FX loss of $380 million, the majority of which was unrealized (2023 - unrealized FX gain of $194 million; 2022 - unrealized FX loss of $471 million) (see Note 8). Mexican Peso-U.S dollar FX Forward contracts The Company’s Mexican subsidiaries have net U.S. dollar-denominated monetary assets or liabilities which, for Mexican income tax purposes, are subject to periodic revaluation based on changes in the value of the Mexican peso ("Ps.") against the U.S. dollar. This revaluation creates fluctuations in the Company’s Mexican income tax expense and the amount of income taxes paid in Mexican pesos. The Company also has net monetary assets or liabilities denominated in Mexican pesos that are subject to periodic re-measurement and settlement that create fluctuations within "Other (income) expense". Until January 2024, the Company hedged its net exposure to Mexican peso/U.S. dollar fluctuations in earnings with foreign currency forward contracts. The foreign currency forward contracts involved the Company’s agreement to buy or sell pesos at an agreed-upon exchange rate on a future date. The Company measures the foreign currency derivative contracts at fair value each period and recognizes any change in "Other (income) expense". The cash flows associated with these instruments are classified as "Operating activities" within the Company's Consolidated Statements of Cash Flows. During the year, the Company recorded a loss of $4 million related to foreign exchange currency forwards prior to settlement (2023 - loss of $39 million). As of January 12, 2024, the Company settled all outstanding foreign currency forward contracts, resulting in a cash outflow of $65 million. As at December 31, 2023, the fair value of outstanding foreign exchange contracts included in "Accounts payable and accrued liabilities" was $60 million. Offsetting The Company’s foreign currency forward contracts are executed with counterparties in the U.S. and were governed by International Swaps and Derivatives Association agreements that included standard netting arrangements. Asset and liability positions from contracts with the same counterparty were net settled upon maturity/expiration and presented on a net basis in the Company's Consolidated Balance Sheets prior to settlement. Interest rate management The Company is exposed to interest rate risk, which is the risk that the fair value or future cash flows of a financial instrument will vary as a result of changes in market interest rates. In order to manage funding needs or capital structure goals, the Company enters into debt or finance lease agreements that are subject to either fixed market interest rates set at the time of issue or floating rates determined by ongoing market conditions. Debt subject to variable interest rates exposes the Company to variability in interest expense, while debt subject to fixed interest rates exposes the Company to variability in the fair value of debt. To manage interest rate exposure, the Company accesses diverse sources of financing and manages borrowings in line with a targeted range of capital structure, debt ratings, liquidity needs, maturity schedule, and currency and interest rate profiles. In anticipation of future debt issuances, the Company may enter into forward rate agreements that are designated as cash flow hedges, to substantially lock in all or a portion of the effective future interest expense. The Company may also enter into swap and lock agreements, designated as fair value hedges, to manage the mix of fixed and floating rate debt. Designated hedges that were previously settled were amortized from AOCI to "Net interest expense" for a total of $6 million in the year ended December 31, 2024 (2023 - $7 million; 2022 - $6 million).

The Company categorizes its financial assets and liabilities measured at fair value into a three-level hierarchy that prioritizes those inputs to valuation techniques used to measure fair value based on the degree to which they are observable. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices in active markets for identical assets and liabilities; Level 2 inputs, other than quoted prices included within Level 1, are observable for the asset or liability either directly or indirectly; and Level 3 inputs are not observable in the market.

The Company’s short-term financial instruments include cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities, and short-term borrowings including commercial paper and term loans. The carrying value of short-term financial instruments approximate their fair values.

The carrying value of the Company’s debt does not approximate its fair value. The estimated fair value has been determined based on market information where available, or by discounting future payments of principal and interest at estimated interest rates expected to be available to the Company at period end. All measurements are classified as Level 2. The Company’s long-term debt, including current maturities, with a carrying value of $20,749 million as at December 31, 2024 (December 31, 2023 - $21,437 million), had a fair value of $18,911 million (December 31, 2023 - $20,550 million).

Derivative financial instruments may be used to selectively reduce volatility associated with fluctuations in interest rates, FX rates, the price of fuel, and stock-based compensation expense. Where derivatives are designated as hedging instruments, the relationship between the hedging instruments and their associated hedged items is documented, as well as the risk management objective and strategy for the use of the hedging instruments. This documentation includes linking the derivatives that are designated as fair value or cash flow hedges to specific assets or liabilities on the Company's Consolidated Balance Sheets, commitments, or forecasted transactions. At the time a derivative contract is entered into and at least quarterly thereafter, an assessment is made as to whether the derivative item is effective in offsetting the changes in fair value or cash flows of the hedged items. The derivative qualifies for hedge accounting treatment if it is effective in substantially mitigating the risk it was designed to address.

The railway industry predominantly serves financially established customers, and the Company has experienced limited financial losses with respect to credit risk. The credit worthiness of customers is assessed using credit scores supplied by a third party and through direct monitoring of their financial well-being on a continual basis. The Company establishes guidelines for customer credit limits and should thresholds in these areas be reached, appropriate precautions are taken to improve collectability.

Counterparties to financial instruments expose the Company to credit losses in the event of non-performance. Counterparties for derivative and cash transactions are limited to high credit quality financial institutions, which are monitored on an ongoing basis. Counterparty credit assessments are based on the financial health of the institutions and their credit ratings from external agencies. The Company does not anticipate non-performance that would materially impact the Company’s Consolidated Financial Statements. In addition, the Company believes there are no significant concentrations of credit risk.

The Company conducts business transactions and owns assets in Canada, the U.S., and Mexico. As a result, the Company is exposed to fluctuations in the value of financial commitments, assets, liabilities, income, or cash flows due to changes in FX rates. The Company may enter into FX risk management transactions primarily to manage fluctuations in the exchange rate between Canadian and U.S. currencies, along with fluctuations in the Mexican peso and U.S dollar as discussed below in "Foreign currency derivative instruments". FX exposure is primarily mitigated through natural offsets created by revenues, expenditures, and balance sheet positions incurred in the same currency. Where appropriate, the Company may negotiate with customers and suppliers to reduce the net exposure.

The majority of the Company’s U.S. dollar-denominated long-term debt, finance lease obligations, and operating lease liabilities have been designated as a hedge of the Company's net investment in foreign subsidiaries. This designation has the effect of mitigating volatility on Net income by offsetting long-term FX gains and losses on U.S. dollar-denominated long-term debt and gains and losses on its net investment. The effect of the Company's net investment hedge recognized in “Other comprehensive income (loss)” in 2024 was an FX loss of $380 million, the majority of which was unrealized (2023 - unrealized FX gain of $194 million; 2022 - unrealized FX loss of $471 million) (see Note 8).

The Company’s Mexican subsidiaries have net U.S. dollar-denominated monetary assets or liabilities which, for Mexican income tax purposes, are subject to periodic revaluation based on changes in the value of the Mexican peso ("Ps.") against the U.S. dollar. This revaluation creates fluctuations in the Company’s Mexican income tax expense and the amount of income taxes paid in Mexican pesos. The Company also has net monetary assets or liabilities denominated in Mexican pesos that are subject to periodic re-measurement and settlement that create fluctuations within "Other (income) expense". Until January 2024, the Company hedged its net exposure to Mexican peso/U.S. dollar fluctuations in earnings with foreign currency forward contracts. The foreign currency forward contracts involved the Company’s agreement to buy or sell pesos at an agreed-upon exchange rate on a future date.

The Company measures the foreign currency derivative contracts at fair value each period and recognizes any change in "Other (income) expense". The cash flows associated with these instruments are classified as "Operating activities" within the Company's Consolidated Statements of Cash Flows.

During the year, the Company recorded a loss of $4 million related to foreign exchange currency forwards prior to settlement (2023 - loss of $39 million). As of January 12, 2024, the Company settled all outstanding foreign currency forward contracts, resulting in a cash outflow of $65 million. As at December 31, 2023, the fair value of outstanding foreign exchange contracts included in "Accounts payable and accrued liabilities" was $60 million.

The Company’s foreign currency forward contracts are executed with counterparties in the U.S. and were governed by International Swaps and Derivatives Association agreements that included standard netting arrangements. Asset and liability positions from contracts with the same counterparty were net settled upon maturity/expiration and presented on a net basis in the Company's Consolidated Balance Sheets prior to settlement.

The Company is exposed to interest rate risk, which is the risk that the fair value or future cash flows of a financial instrument will vary as a result of changes in market interest rates. In order to manage funding needs or capital structure goals, the Company enters into debt or finance lease agreements that are subject to either fixed market interest rates set at the time of issue or floating rates determined by ongoing market conditions. Debt subject to variable interest rates exposes the Company to variability in interest expense, while debt subject to fixed interest rates exposes the Company to variability in the fair value of debt.

To manage interest rate exposure, the Company accesses diverse sources of financing and manages borrowings in line with a targeted range of capital structure, debt ratings, liquidity needs, maturity schedule, and currency and interest rate profiles. In anticipation of future debt issuances, the Company may enter into forward rate agreements that are designated as cash flow hedges, to substantially lock in all or a portion of the effective future interest expense. The Company may also enter into swap and lock agreements, designated as fair value hedges, to manage the mix of fixed and floating rate debt.