Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2016
Accounting Policies [Abstract]
Accounting principles generally accepted in the United States of America (GAAP)	These consolidated financial statements are expressed in Canadian dollars and have been prepared in accordance with GAAP.
Principles of consolidation	These consolidated financial statements include the accounts of CP and all its subsidiaries. The Company’s investments in which it has significant influence are accounted for using the equity method. All intercompany accounts and transactions have been eliminated.
Use of estimates	The preparation of these consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of revenues and expenses during the year, the reported amounts of assets and liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements. Management regularly reviews its estimates, including those related to environmental liabilities, pensions and other benefits, depreciable lives of properties, deferred income tax assets and liabilities, as well as legal and personal injury liabilities based upon currently available information. Actual results could differ from these estimates.
Revenue recognition	Railway freight revenues are recognized based on the percentage of completed service method. The allocation of revenue between reporting periods is based on the relative transit time in each reporting period with expenses recognized as incurred. Volume rebates to customers are accrued as a reduction of freight revenues based on estimated volume and contract terms as freight service is provided. Other revenues, including passenger revenue, revenue from leasing certain assets, switching fees, and revenue from logistics services, are recognized as service is performed or contractual obligations are met. Revenues are presented net of taxes collected from customers and remitted to government authorities.
Cash and cash equivalents	Cash and cash equivalents include highly liquid short-term investments that are readily convertible to cash with original maturities of three months or less, but exclude cash and cash equivalents subject to restrictions.
Restricted cash and cash equivalents	Cash and cash equivalents that are restricted as to withdrawal or usage, in accordance with specific agreements, are presented as restricted cash and cash equivalents on the balance sheets when applicable.
Foreign currency translation	Assets and liabilities denominated in foreign currencies, other than those held through foreign subsidiaries, are translated into Canadian dollars at the year-end exchange rate for monetary items and at the historical exchange rates for non-monetary items. Foreign currency revenues and expenses are translated at the exchange rates in effect on the dates of the related transactions. Foreign exchange ("FX") gains and losses, other than those arising from the translation of the Company’s net investment in foreign subsidiaries, are included in income. The accounts of the Company’s foreign subsidiaries are translated into Canadian dollars using the year-end exchange rate for assets and liabilities and the average exchange rates during the year for revenues, expenses, gains and losses. FX gains and losses arising from the translation of the foreign subsidiaries’ assets and liabilities are included in “Other comprehensive income (loss)”. A portion of U.S. dollar-denominated long-term debt has been designated as a hedge of the net investment in foreign subsidiaries. As a result, unrealized FX gains and losses on U.S. dollar-denominated long-term debt, designated as a hedge, are offset against FX gains and losses arising from the translation of foreign subsidiaries’ accounts in “Other comprehensive income (loss)”.
Pensions and other benefits	Pension costs are actuarially determined using the projected-benefit method pro-rated over the credited service periods of employees. This method incorporates management’s best estimates of expected plan investment performance, salary escalation and retirement ages of employees. The expected return on fund assets is calculated using market-related asset values developed from a five-year average of market values for the fund’s public equity securities and absolute return strategies (with each prior year’s market value adjusted to the current date for assumed investment income during the intervening period) plus the market value of the fund’s fixed income, real estate and infrastructure securities, subject to the market-related asset value not being greater than 120% of the market value nor being less than 80% of the market value. The discount rate used to determine the projected-benefit obligation is based on blended market interest rates on high-quality corporate debt instruments with matching cash flows. Unrecognized actuarial gains and losses in excess of 10% of the greater of the benefit obligation and the market-related value of plan assets are amortized over the expected average remaining service period of active employees expected to receive benefits under the plan (approximately 11 years). Prior service costs arising from collectively bargained amendments to pension plan benefit provisions are amortized over the term of the applicable union agreement. Prior service costs arising from all other sources are amortized over the expected average remaining service period of active employees who are expected to receive benefits under the plan at the date of amendment. Costs for post-retirement and post-employment benefits other than pensions, including post-retirement health care and life insurance and some workers’ compensation and long-term disability benefits in Canada, are actuarially determined on a basis similar to pension costs. The over or under funded status of defined benefit pension and other post-retirement benefit plans are measured as the difference between the fair value of the plan assets and the benefit obligation, and are recognized on the balance sheets. In addition, any unrecognized actuarial gains and losses and prior service costs and credits that arise during the period are recognized as a component of “Other comprehensive income (loss)”, net of tax. Gains and losses on post-employment benefits that do not vest or accumulate, including some workers’ compensation and long-term disability benefits in Canada, are included immediately in income as “Compensation and benefits”.
Materials and supplies	Materials and supplies are carried at the lower of average cost or market value and consist primarily of fuel and parts used in the repair and maintenance of track structures, equipment, locomotives and freight cars.
Properties	Fixed asset additions and major renewals are recorded at cost, including direct costs, attributable indirect costs and carrying costs, less accumulated depreciation and any impairment. When there is a legal obligation associated with the retirement of property, a liability is initially recognized at its fair value and a corresponding asset retirement cost is added to the gross book value of the related asset and amortized to expense over the estimated term to retirement. The Company reviews the carrying amounts of its properties whenever changes in circumstances indicate that such carrying amounts may not be recoverable based on future undiscounted cash flows. When such properties are determined to be impaired, recorded asset values are revised to their fair value. The Company recognizes expenditures as additions to properties or operating expenses based on whether the expenditures increase the output or service capacity, lower the associated operating costs or extend the useful life of the properties and whether the expenditures exceed minimum physical and financial thresholds. Much of the additions to properties, both new and replacement properties, are self-constructed. These are initially recorded at cost, including direct costs and attributable indirect costs, overheads and carrying costs. Direct costs include, among other things, labour costs, purchased services, equipment costs and material costs. Attributable indirect costs and overheads include incremental long-term variable costs resulting from the execution of capital projects. Indirect costs mainly include work trains, material distribution, highway vehicles and work equipment. Overheads primarily include a portion of the engineering department’s costs, which plans, designs and administers these capital projects. These costs are allocated to projects by applying a measure consistent with the nature of the cost, based on cost studies. For replacement properties, the project costs are allocated to dismantling and installation based on cost studies. Dismantling work is performed concurrently with the installation. Ballast programs including undercutting, shoulder ballasting and renewal programs that form part of the annual track program are capitalized as this work, and the related added ballast material, significantly improves drainage, which in turn extends the life of ties and other track materials. These costs are tracked separately from the underlying assets and depreciated over the period to the next estimated similar ballast program. Spot replacement of ballast is considered a repair which is expensed as incurred. The costs of large refurbishments are capitalized and locomotive overhauls are expensed as incurred, except where overhauls represent a betterment of the locomotive in which case costs are capitalized. The Company capitalizes development costs for major new computer systems. The Company follows group depreciation which groups assets which are similar in nature and have similar economic lives. The property groups are depreciated on a straight-line basis reflecting their expected economic lives determined by studies of historical retirements of properties in the group and engineering estimates of changes in current operations and of technological advances. Actual use and retirement of assets may vary from current estimates, which would impact the amount of depreciation expense recognized in future periods. Rail and other track material in the U.S. are depreciated based directly on usage. When depreciable property is retired or otherwise disposed of in the normal course of business, the book value, less net salvage proceeds, is charged to accumulated depreciation and if different than the assumptions under the depreciation study could potentially result in adjusted depreciation expense over a period of years. However, when removal costs exceed the salvage value on assets and the Company has no legal obligation to remove the assets, the removal costs incurred are charged to income in the period in which the assets are removed and are not charged to accumulated depreciation. For the sale or retirement of larger groups of depreciable assets that are unusual and were not considered in depreciation studies, CP records a gain or loss for the difference between net proceeds and net book value of the assets sold or retired. Equipment under capital lease is included in Properties and depreciated over the period of expected use.
Assets held for sale	Assets to be disposed that meet the held for sale criteria are reported at the lower of their carrying amount and fair value, less costs to sell, and are no longer depreciated.
Goodwill and intangible assets	Goodwill represents the excess of the purchase price over the fair value of identifiable net assets upon acquisition of a business. Goodwill is assigned to the reporting units that are expected to benefit from the business acquisition which, after integration of operations with the railway network, may be different than the acquired business. The carrying value of goodwill, which is not amortized, is assessed for impairment annually in the fourth quarter of each year as at October 1^st, or more frequently as economic events dictate. The Company has the option of performing an assessment of certain qualitative factors (“Step 0”) to determine if it is more likely than not that the fair value of a reporting unit is less than its carrying value or proceeding directly to a quantitative impairment test (“Step 1”). Qualitative factors include but are not limited to, economic, market and industry conditions, cost factors and overall financial performance of the reporting unit. If Step 0 indicates that the carrying value is less than the fair value, then performing the two-step impairment test is unnecessary. Under Step 1, the fair value of the reporting unit is compared to its carrying value, including goodwill. If the fair value of the reporting unit is less than its carrying value, goodwill is potentially impaired. The impairment charge that would be recognized is the excess of the carrying value of the goodwill over the fair value of the goodwill, determined in the same manner as in a business combination. Intangible assets with finite lives are amortized on a straight-line basis over the estimated useful lives of the respective assets. Favourable leases, customer relationships and interline contracts have amortization periods ranging from 15 to 20 years. When there is a change in the estimated useful life of an intangible asset with a finite life, amortization is adjusted prospectively.
Financial instruments	Financial instruments are contracts that give rise to a financial asset of one party and a financial liability or equity instrument of another party. Financial instruments are recognized initially at fair value, which is the amount of consideration that would be agreed upon in an arm’s-length transaction between willing parties. Subsequent measurement depends on how the financial instruments have been classified. Accounts receivable and investments, classified as loans and receivables, are measured at amortized cost, using the effective interest method. Cash and cash equivalents and derivatives are classified as held for trading and are measured at fair value. Accounts payable, accrued liabilities, short-term borrowings, dividends payable, other long-term liabilities and long-term debt, classified as other liabilities, are also measured at amortized cost.
Derivative financial instruments	Derivative financial and commodity instruments may be used from time to time by the Company to manage its exposure to risks relating to foreign currency exchange rates, stock-based compensation, interest rates and fuel prices. When CP utilizes derivative instruments in hedging relationships, CP identifies, designates and documents those hedging transactions and regularly tests the transactions to demonstrate effectiveness in order to continue hedge accounting. All derivative instruments are classified as held for trading and recorded at fair value. Any change in the fair value of derivatives not designated as hedges is recognized in the period in which the change occurs in the Consolidated Statements of Income in the line item to which the derivative instrument is related. On the Consolidated Balance Sheets they are classified in “Other assets”, “Other long-term liabilities”, “Other current assets” or “Accounts payable and accrued liabilities” as applicable. Gains and losses arising from derivative instruments may affect the following lines on the Consolidated Statements of Income: “Revenues”, “Compensation and benefits”, “Fuel”, “Other income and charges”, and “Net interest expense”. For fair value hedges, the periodic changes in values are recognized in income, on the same line as the changes in values of the hedged items are also recorded. For a cash flow hedge, the change in value of the effective portion is recognized in “Other comprehensive income (loss)”. Any ineffectiveness within an effective cash flow hedge is recognized in income as it arises in the same income account as the hedged item. Should a cash flow hedging relationship become ineffective, previously unrealized gains and losses remain within “Accumulated other comprehensive loss” until the hedged item is settled and, prospectively, future changes in value of the derivative are recognized in income. The change in value of the effective portion of a cash flow hedge remains in “Accumulated other comprehensive loss” until the related hedged item settles, at which time amounts recognized in “Accumulated other comprehensive loss” are reclassified to the same income or balance sheet account that records the hedged item. In the Consolidated Statements of Cash Flows, cash flows relating to derivative instruments designated as hedges are included in the same line as the related hedged items.
Environmental remediation	Environmental remediation accruals, recorded on an undiscounted basis unless a reliably determinable estimate as to amount and timing of costs can be established, cover site-specific remediation programs. The accruals are recorded when the costs to remediate are probable and reasonably estimable. Certain future costs to monitor sites are discounted at an adjusted risk free rate. Provisions for environmental remediation costs are recorded in “Other long-term liabilities”, except for the current portion, which is recorded in “Accounts payable and accrued liabilities”.
Income taxes	The Company follows the liability method of accounting for income taxes. Deferred income tax assets and liabilities are determined based on differences between the financial reporting and tax bases of assets and liabilities using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The effect of a change in income tax rates on deferred income tax assets and liabilities is recognized in income in the period during which the change occurs. When appropriate, the Company records a valuation allowance against deferred tax assets to reflect that these tax assets may not be realized. In determining whether a valuation allowance is appropriate, CP considers whether it is more likely than not that all or some portion of CP’s deferred tax assets will not be realized, based on management’s judgment using available evidence about future events. At times, tax benefit claims may be challenged by a tax authority. Tax benefits are recognized only for tax positions that are more likely than not sustainable upon examination by tax authorities. The amount recognized is measured as the largest amount of benefit that is greater than 50% likely to be realized upon settlement. A liability for “unrecognized tax benefits” is recorded for any tax benefits claimed in CP’s tax returns that do not meet these recognition and measurement standards. Investment and other similar tax credits are deferred on the Consolidated Balance Sheets and amortized to “Income tax expense” as the related asset is recognized in income.
Earnings per share	Basic earnings per share are calculated using the weighted average number of common shares outstanding during the year. Diluted earnings per share are calculated using the treasury stock method for determining the dilutive effect of options.
Stock-based compensation	CP follows the fair value based approach to account for stock options. Compensation expense and an increase in “Additional paid-in capital” are recognized for stock options over their vesting period, or over the period from the grant date to the date employees become eligible to retire when this is shorter than the vesting period, based on their estimated fair values on the grant date, as determined using the Black-Scholes option-pricing model. Any consideration paid by employees on exercise of stock options is credited to “Share capital” when the option is exercised and the recorded fair value of the option is removed from “Additional paid-in capital“ and credited to “Share capital”. Compensation expense is also recognized for deferred share units (“DSUs”), performance share units (“PSUs”) and restricted share units (“RSUs”) using the fair value method. Compensation expense is recognized over the vesting period, or for PSUs and DSUs only, over the period from the grant date to the date employees become eligible to retire when this is shorter than the vesting period. Forfeitures of DSUs, PSUs and RSUs are estimated at issuance and subsequently at the balance sheet date. The employee share purchase plan (“ESPP”) gives rise to compensation expense that is recognized using the issue price by amortizing the cost over the vesting period or over the period from the grant date to the date employees become eligible to retire when this is shorter than the vesting period.
Accounting changes	Implemented in 2016 Early Adoption of Restricted Cash In November 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (“ASU”) 2016-18, Restricted Cash a consensus of the FASB Emerging Issues Task Force under FASB Accounting Standards Codification ("ASC")Topic 230 Statement of Cash Flows. The amendments required the statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash and restricted cash equivalents. Restricted cash will therefore be included in beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The updated standard does not provide a definition of restricted cash and restricted cash equivalents. This ASU is effective retrospectively for public entities for fiscal years and interim periods within those years, beginning on or after December 15, 2017. Early adoption of this ASU is permitted. The Company adopted the provisions of this ASU during the fourth quarter of 2016. As a result of the adoption of ASU 2016-18, the 2014 comparative Statement of Cash Flows has been restated to reflect $411 million in restricted cash and cash equivalents used to collateralize letters of credit in the beginning-of-period total cash and cash equivalents, with the corresponding change in restricted cash and cash equivalents of the year removed from investing activities. There was no restricted cash balance remaining at the end of both comparative periods. Amendments to the Consolidation Analysis In February 2015, the FASB issued ASU 2015-02, Amendments to the Consolidation Analysis under FASB ASC Topic 810 Consolidation. The amendments required reporting entities to evaluate whether they should consolidate certain legal entities under the revised consolidation model. Specifically, the amendments modify the evaluation of whether limited partnerships and similar legal entities are variable interest entities (“VIEs”) or voting interest entities, eliminated the presumption that a general partner should consolidate a limited partnership and affected the consolidation analysis of reporting entities involved with VIEs, particularly those that have fee arrangements and related party relationships. This ASU was effective for public entities for fiscal years, and interim periods within those years, beginning on or after December 15, 2015. Entities had the option of using either a full retrospective or a modified retrospective approach to adopt this ASU. The Company evaluated all existing VIEs and all arrangements that might give rise to a VIE; no changes to consolidation, disclosure or financial statement presentation were required as a result of this evaluation. Future changes Simplifying the Subsequent Measurement of Inventory In July 2015, the FASB issued ASU 2015-11, Simplifying the Measurement of Inventory under FASB ASC Topic 330 Inventory. The amendments require reporting entities to measure inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. The amendments apply to inventory that is measured using the first-in, first-out or average cost basis. This ASU will be effective for public entities for fiscal years, and interim periods within those years, beginning after December 15, 2016, and will be applied prospectively. The Company does not anticipate that the adoption of this ASU will have an impact on the consolidated financial statements. Leases In February 2016, the FASB issued ASU 2016-02, Leases. The new FASB ASC Topic 842 Leases supersedes the lease recognition and measurement requirements in Topic 840 Leases. This new standard requires recognition of right-of-use assets and lease liabilities by lessees for those leases classified as finance and operating leases with a maximum term exceeding 12 months. This ASU will be effective for public entities for fiscal years, and interim periods within those years, beginning on or after December 15, 2018. Entities are required to use a modified retrospective approach to adopt this ASU. The Company is assessing contractual arrangements through a cross functional team and assessing potential system changes required to deliver required accounting changes. There will be a material increase to right of use assets and lease liabilities on the Consolidated balance sheet, but the Company does not anticipate a material impact on the Consolidated statement of income. Revenue from Contracts with Customers In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations under FASB ASC Topic 606. The amendments clarify the principal versus agent guidance in determining whether to recognize revenue on a gross or net basis. The amendments are effective for public entities for annual reporting periods beginning on or after December 15, 2017, including interim periods within that reporting period. Entities have the option of using either a full retrospective or a modified retrospective approach to adopt this ASU. CP is currently assessing the transition methods for adoption in the first quarter of 2018. CP expects to continue to recognize freight revenue, which represents greater than 95% of CP's annual revenues, over time and is currently reviewing agreements to determine the impact of the new standard on non-freight revenue. Compensation – Stock Compensation In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation, under ASC Topic 718. The amendments clarify the guidance relating to treatment of excess tax benefits and deficiencies, acceptable forfeiture rate policies, and treatment of cash paid by an employer when directly withholding shares for tax-withholding purposes and the requirement to treat such cash flows as a financing activity. This ASU will be effective for public entities for fiscal years, and interim periods within those years, beginning on or after December 15, 2016. Early adoption is permitted. The Company does not anticipate the adoption of this ASU will have an impact on the consolidated financial statements.