Financial instruments	12 Months Ended
Dec. 31, 2023
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 long-term 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 $21,437 million as at December 31, 2023 (December 31, 2022 - $19,651 million), had a fair value of $20,550 million (December 31, 2022 - $17,720 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 FX gains and losses on long-term debt are mainly unrealized and can only be realized when U.S. dollar-denominated long-term debt matures or is settled. The Company also has long-term FX exposure on its investment in foreign subsidiaries with a U.S. dollar functional currency. 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 net investment in these 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 net investment hedge recognized in “Other comprehensive (loss) income” in 2023 was an FX gain of $194 million, the majority of which was unrealized (2022 – unrealized loss of $471 million; 2021 – unrealized gain of $25 million) (see Note 8). U.S.dollar- Canadian dollar FX forward contracts During 2021, the Company entered into various FX forward contracts totalling a notional U.S. $1.0 billion to fix the FX rate and lock-in a portion of the amount of Canadian dollars it could have borrowed to finance the U.S. dollar-denominated cash portion of the total consideration payable pursuant to the Original Merger Agreement with KCS. During the third quarter of 2021, the Company settled the FX forward contracts and did not have any such contracts remaining as at December 31, 2021. The realized gain from settlement of the FX forward contracts was $13 million and was recorded in "Other expense" on the Company's Consolidated Statements of Income for the year ended December 31, 2021 (2023 - $nil; 2022 - $nil). Mexican Peso- U.S dollar FX Forward contracts The Company’s Mexican subsidiaries have net U.S. dollar-denominated monetary assets 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 denominated in Mexican pesos that are subject to periodic re-measurement and settlement that create fluctuations within "Other expense". The Company has hedged its net exposure to Mexican peso/U.S. dollar fluctuations in earnings with foreign currency forward contracts. The foreign currency forward contracts involve the Company’s agreement to buy or sell pesos at an agreed-upon exchange rate on a future date. As at December 31, 2023, the Company had outstanding foreign currency forward contracts to purchase a notional value of U.S. $215 million. These outstanding contracts are at a weighted-average exchange rate of Ps.20.61 per U.S. $1.00, and have a maturity date of January 12, 2024. The Company has not designated any of the foreign currency derivative contracts as hedging instruments for accounting purposes. The Company measures the foreign currency derivative contracts at fair value each period and recognizes any change in "Other expense". The cash flows associated with these instruments are classified as "Operating activities" within the Consolidated Statements of Cash Flows. Following the acquisition of control of KCS on April 14, 2023 and through the period ended December 31, 2023, the Company recorded a loss of $39 million related to foreign exchange currency forwards. As at December 31, 2023, the fair value of outstanding foreign exchange contracts included in "Accounts payable and accrued liabilities" was $60 million. On maturity, the Company settled all outstanding foreign currency forward contracts, resulting in a cash payment of $65 million. Offsetting The Company’s foreign currency forward contracts are executed with counterparties in the U.S. and are governed by International Swaps and Derivatives Association agreements that include standard netting arrangements. Asset and liability positions from contracts with the same counterparty are 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. Forward starting swaps In the first half of 2021, the Company entered into forward starting swaps with terms of up to 30 years, totalling a notional U.S. $2.4 billion to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes. On May 21, 2021, the Original Merger Agreement with KCS was terminated which resulted in the Company ceasing hedge accounting for the U.S. $2.4 billion of forward starting swaps. However, as the note issuances were still reasonably possible to occur, fair value losses of $73 million prior to this determination remained in AOCI, net of tax. Fair value losses of $251 million during the period from May 21, 2021 through to the roll and re-designation described below were recorded within “Other Expense" on the Company’s Consolidated Statements of Income for the year ended December 31, 2021. Following CP entering into the Merger Agreement with KCS, the Company rolled the notional U.S. $2.4 billion of forward starting swaps but did not effect a cash settlement. Concurrently, the Company re-designated the forward starting swaps totalling U.S. $2.4 billion to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes. The changes in fair value on the forward starting swaps were recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the notes were issued. Fair value gains subsequent to re-designation of $94 million were recorded within “Other comprehensive income” on the Company’s Consolidated Statements of Comprehensive Income for the year ended December 31, 2021. During the fourth quarter of 2021, the Company cash settled all outstanding forward starting swaps related to debt issuances that occurred in the same period. The fair value of these derivative instruments at the time of settlement was a loss of $230 million. The related $21 million gain within "Accumulated other comprehensive loss" will be reclassified to "Net interest expense" ratably over the duration of the notes' hedged interest payments. Bond locks In the first quarter of 2021, the Company entered into seven-year interest rate bond locks totalling a notional $600 million to fix the benchmark rate on cash flows associated with a highly probable forecasted issuance of long-term notes. On May 21, 2021, the Original Merger Agreement with KCS was terminated which resulted in the Company ceasing hedge accounting for the $600 million of bond locks. However, as the note issuances were still reasonably possible to occur, fair value losses of $2 million prior to this determination remained in “Accumulated other comprehensive loss”, net of tax. Fair value losses of $10 million during the period from May 21, 2021 through to the roll and re-designation described below were recorded within “Other expense" on the Company’s Consolidated Statements of Income for the year ended December 31, 2021. Following CP entering into the Merger Agreement with KCS, the Company rolled the notional $600 million of bond locks but did not effect a cash settlement. Concurrently, the Company re-designated the bond locks totalling $600 million to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes. The changes in fair value on the bond locks are recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the notes were issued. Fair value gains subsequent to re-designation of $19 million were recorded within “Other comprehensive income” on the Company’s Consolidated Statements of Comprehensive Income for the year ended December 31, 2021. During the fourth quarter of 2021, the Company cash settled all outstanding bond locks related to debt issuances that occurred in the same period. The fair value of these derivative instruments at the time of settlement was a gain of $7 million. The related $17 million gain within "Accumulated other comprehensive loss" will be reclassified to "Net interest expense" ratably over the duration of the notes' hedged interest payments. Designated hedges that were previously settled were amortized from AOCI to "Net interest expense" for a total of $7 million in the year ended December 31, 2023 (2022 - $6 million; 2021 - $10 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 long-term 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 $21,437 million as at December 31, 2023 (December 31, 2022 - $19,651 million), had a fair value of $20,550 million (December 31, 2022 - $17,720 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 FX gains and losses on long-term debt are mainly unrealized and can only be realized when U.S. dollar-denominated long-term debt matures or is settled. The Company also has long-term FX exposure on its investment in foreign subsidiaries with a U.S. dollar functional currency. 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 net investment in these 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 net investment hedge recognized in “Other comprehensive (loss) income” in 2023 was an FX gain of $194 million, the majority of which was unrealized (2022 – unrealized loss of $471 million; 2021 – unrealized gain of $25 million) (see Note 8).

During 2021, the Company entered into various FX forward contracts totalling a notional U.S. $1.0 billion to fix the FX rate and lock-in a portion of the amount of Canadian dollars it could have borrowed to finance the U.S. dollar-denominated cash portion of the total consideration payable pursuant to the Original Merger Agreement with KCS. During the third quarter of 2021, the Company settled the FX forward contracts and did not have any such contracts remaining as at December 31, 2021. The realized gain from settlement of the FX forward contracts was $13 million and was recorded in "Other expense" on the Company's Consolidated Statements of Income for the year ended December 31, 2021 (2023 - $nil; 2022 - $nil).

The Company’s Mexican subsidiaries have net U.S. dollar-denominated monetary assets 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 denominated in Mexican pesos that are subject to periodic re-measurement and settlement that create fluctuations within "Other expense". The Company has hedged its net exposure to Mexican peso/U.S. dollar fluctuations in earnings with foreign currency forward contracts. The foreign currency forward contracts involve the Company’s agreement to buy or sell pesos at an agreed-upon exchange rate on a future date.

As at December 31, 2023, the Company had outstanding foreign currency forward contracts to purchase a notional value of U.S. $215 million. These outstanding contracts are at a weighted-average exchange rate of Ps.20.61 per U.S. $1.00, and have a maturity date of January 12, 2024. The Company has not designated any of the foreign currency derivative contracts as hedging instruments for accounting purposes. The Company measures the foreign currency derivative contracts at fair value each period and recognizes any change in "Other expense". The cash flows associated with these instruments are classified as "Operating activities" within the Consolidated Statements of Cash Flows.

Following the acquisition of control of KCS on April 14, 2023 and through the period ended December 31, 2023, the Company recorded a loss of $39 million related to foreign exchange currency forwards. As at December 31, 2023, the fair value of outstanding foreign exchange contracts included in "Accounts payable and accrued liabilities" was $60 million. On maturity, the Company settled all outstanding foreign currency forward contracts, resulting in a cash payment of $65 million.

The Company’s foreign currency forward contracts are executed with counterparties in the U.S. and are governed by International Swaps and Derivatives Association agreements that include standard netting arrangements. Asset and liability positions from contracts with the same counterparty are 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.

In the first half of 2021, the Company entered into forward starting swaps with terms of up to 30 years, totalling a notional U.S. $2.4 billion to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes.

On May 21, 2021, the Original Merger Agreement with KCS was terminated which resulted in the Company ceasing hedge accounting for the U.S. $2.4 billion of forward starting swaps. However, as the note issuances were still reasonably possible to occur, fair value losses of $73 million prior to this determination remained in AOCI, net of tax. Fair value losses of $251 million during the period from May 21, 2021 through to the roll and re-designation described below were recorded within “Other Expense" on the Company’s Consolidated Statements of Income for the year ended December 31, 2021.

Following CP entering into the Merger Agreement with KCS, the Company rolled the notional U.S. $2.4 billion of forward starting swaps but did not effect a cash settlement. Concurrently, the Company re-designated the forward starting swaps totalling U.S. $2.4 billion to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes. The changes in fair value on the forward starting swaps were recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the notes were issued. Fair value gains subsequent to re-designation of $94 million were recorded within “Other comprehensive income” on the Company’s Consolidated Statements of Comprehensive Income for the year ended December 31, 2021.

During the fourth quarter of 2021, the Company cash settled all outstanding forward starting swaps related to debt issuances that occurred in the same period. The fair value of these derivative instruments at the time of settlement was a loss of $230 million. The related $21 million gain within "Accumulated other comprehensive loss" will be reclassified to "Net interest expense" ratably over the duration of the notes' hedged interest payments.

In the first quarter of 2021, the Company entered into seven-year interest rate bond locks totalling a notional $600 million to fix the benchmark rate on cash flows associated with a highly probable forecasted issuance of long-term notes.

On May 21, 2021, the Original Merger Agreement with KCS was terminated which resulted in the Company ceasing hedge accounting for the $600 million of bond locks. However, as the note issuances were still reasonably possible to occur, fair value losses of $2 million prior to this determination remained in “Accumulated other comprehensive loss”, net of tax. Fair value losses of $10 million during the period from May 21, 2021 through to the roll and re-designation described below were recorded within “Other expense" on the Company’s Consolidated Statements of Income for the year ended December 31, 2021.

Following CP entering into the Merger Agreement with KCS, the Company rolled the notional $600 million of bond locks but did not effect a cash settlement. Concurrently, the Company re-designated the bond locks totalling $600 million to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes. The changes in fair value on the bond locks are recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the notes were issued. Fair value gains subsequent to re-designation of $19 million were recorded within “Other comprehensive income” on the Company’s Consolidated Statements of Comprehensive Income for the year ended December 31, 2021.

During the fourth quarter of 2021, the Company cash settled all outstanding bond locks related to debt issuances that occurred in the same period. The fair value of these derivative instruments at the time of settlement was a gain of $7 million. The related $17 million gain within "Accumulated other comprehensive loss" will be reclassified to "Net interest expense" ratably over the duration of the notes' hedged interest payments.