Financial Instruments	3 Months Ended
Mar. 31, 2016
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 in line with the fair value hierarchy established by GAAP that prioritizes, with respect to reliability, the inputs to valuation techniques used to measure fair value. This hierarchy consists of three broad levels. Level 1 inputs consist of quoted prices (unadjusted) in active markets for identical assets and liabilities and give the highest priority to these inputs. Level 2 and 3 inputs are based on significant other observable inputs and significant unobservable inputs, respectively, and give lower priority to these inputs. When possible, the estimated fair value is based on quoted market prices and, if not available, estimates from third party brokers. For non-exchange traded derivatives classified in Level 2, the Company uses standard valuation techniques to calculate fair value. Primary inputs to these techniques include observable market prices (interest, foreign exchange (“FX”) and commodity) and volatility, depending on the type of derivative and nature of the underlying risk. The Company uses inputs and data used by willing market participants when valuing derivatives and considers its own credit default swap spread as well as those of its counterparties in its determination of fair value. The carrying values of financial instruments equal or approximate their fair values with the exception of long-term debt which has a fair value of approximately $9,491 million at March 31, 2016 (December 31, 2015 - $9,750 million) and a carrying value of $8,453 (December 31, 2015 - $8,957 million). The estimated fair value of current and long-term borrowings has been determined based on market information where available, or by discounting future payments of interest and principal at estimated interest rates expected to be available to the Company at period end. All derivatives and long-term debt are classified as Level 2. 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 Interim 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 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. FX management The Company conducts business transactions and owns assets in both Canada and the United States. As a result, the Company is exposed to fluctuations in 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. 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 U.S. affiliates. The majority of the Company’s U.S. dollar denominated long-term debt has been designated as a hedge of the 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 effective portion recognized in “Other comprehensive (loss) income” for the three months ended March 31, 2016 was an unrealized FX gain of $308 million (three months ended March 31, 2015 - unrealized FX loss of $356 million). There was no ineffectiveness during the three months ended March 31, 2016 and March 31, 2015. 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 capital lease agreements that are subject to either fixed market interest rates set at the time of issue or floating rates determined by on-going 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 agreements, designated as fair value hedges, to manage the mix of fixed and floating rate debt. Forward starting swaps During the fourth quarter of 2014, the Company entered into forward starting floating-to-fixed interest rate swap agreements (“forward starting swaps”) totaling a notional U.S. $1.4 billion to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes. The effective portion of changes in fair value on the forward starting swaps is recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the probable forecasted notes are issued. Subsequent to the notes issuance, amounts in “Accumulated other comprehensive loss” are reclassified to “Net interest expense”. During the first quarter of 2015, the Company settled a notional U.S. $700 million of forward starting swaps related to the U.S. $700 million 2.900% 10-year notes issued in the same period. The fair value of these derivative instruments was a loss of U.S. $50 million ($63 million) at the time of settlement. The effective portion of changes in fair value on the forward starting swaps of U.S. $48 million ($60 million), was recorded in “Accumulated other comprehensive loss”, and is amortized to “Net interest expense” over the term of the underlying hedged notes. During the three months ended March 31, 2016, a loss of $1 million related to these previously settled derivatives has been amortized to “Net interest expense” (three months ended March 31, 2015 - loss of $1 million). The Company expects that during the next 12 months $6 million of losses will be amortized to “Net interest expense”. The ineffective portion of U.S. $2 million ($2 million) was recorded immediately in income as “Net interest expense” during the first quarter of 2015. During the third quarter of 2015, the Company de-designated the hedging relationship for U.S. $700 million of forward starting swaps related to a portion of the U.S. $900 million 6.125% 100-year notes issued. The Company did not cash settle these swaps and therefore recorded a non-cash loss of U.S. $36 million ($47 million) at the time of de-designation. The effective portion of changes in fair value of the de-designated forward starting swaps of U.S. $36 million ($47 million) was recorded in “Accumulated other comprehensive loss” and is amortized to “Net interest expense” over the first 10 years as the underlying interest expense payments, which are hedged, of the U.S. $900 million notes are made. During the three months ended March 31, 2016, a loss of $1 million related to these previously de-designated derivatives has been amortized to “Net interest expense”. The Company expects that during the next 12 months $5 million of losses will be amortized to “Net interest expense”. There was no ineffectiveness to record upon de-designation. During the third quarter of 2015, the Company re-designated the forward starting swaps totalling U.S. $700 million to fix the benchmark rate on cash flows associated with a highly probable forecasted issuance of long-term notes. The effective portion of changes in fair value from the re-designation date on the forward starting swaps is recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the probable forecasted notes are issued. Subsequent to the notes being issued, amounts in “Accumulated other comprehensive loss” will be amortized to “Net interest expense”. As at March 31, 2016, the total fair value loss of $112 million derived from the remaining forward starting swaps was included in “Accounts payable and accrued liabilities” of which $65 million relates to the re-designated existing forward starting swaps. The effective portion of $63 million on the re-designated existing forward starting swaps is reflected in “Other comprehensive (loss) income” and the ineffective portion of $2 million is recorded to “Net interest expense” on the Consolidated Statements of Comprehensive Income and the Consolidated Statements of Income, respectively. As at December 31, 2015, the total fair value loss of $60 million derived from the remaining forward starting swaps was included in "Accounts payable and accrued liabilities" of which $13 million related to the re-designated existing forward starting swaps. The effective portion of $13 million on the re-designated existing forward starting swaps was reflected in "Other comprehensive income" and the negligible ineffective portion was recorded to "Net interest expense" on the Consolidated Statements of Comprehensive Income and the Consolidated Statements of Income, respectively.

Financial instruments

A. Fair values of financial instruments

The Company categorizes its financial assets and liabilities measured at fair value in line with the fair value hierarchy established by GAAP that prioritizes, with respect to reliability, the inputs to valuation techniques used to measure fair value. This hierarchy consists of three broad levels. Level 1 inputs consist of quoted prices (unadjusted) in active markets for identical assets and liabilities and give the highest priority to these inputs. Level 2 and 3 inputs are based on significant other observable inputs and significant unobservable inputs, respectively, and give lower priority to these inputs.

When possible, the estimated fair value is based on quoted market prices and, if not available, estimates from third party brokers. For non-exchange traded derivatives classified in Level 2, the Company uses standard valuation techniques to calculate fair value. Primary inputs to these techniques include observable market prices (interest, foreign exchange (“FX”) and commodity) and volatility, depending on the type of derivative and nature of the underlying risk. The Company uses inputs and data used by willing market participants when valuing derivatives and considers its own credit default swap spread as well as those of its counterparties in its determination of fair value.

The carrying values of financial instruments equal or approximate their fair values with the exception of long-term debt which has a fair value of approximately $9,491 million at March 31, 2016 (December 31, 2015 - $9,750 million) and a carrying value of $8,453 (December 31, 2015 - $8,957 million). The estimated fair value of current and long-term borrowings has been determined based on market information where available, or by discounting future payments of interest and principal at estimated interest rates expected to be available to the Company at period end. All derivatives and long-term debt are classified as Level 2.

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 Interim 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 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.

FX management

The Company conducts business transactions and owns assets in both Canada and the United States. As a result, the Company is exposed to fluctuations in 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. 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 U.S. affiliates. The majority of the Company’s U.S. dollar denominated long-term debt has been designated as a hedge of the 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 effective portion recognized in “Other comprehensive (loss) income” for the three months ended March 31, 2016 was an unrealized FX gain of $308 million (three months ended March 31, 2015 - unrealized FX loss of $356 million). There was no ineffectiveness during the three months ended March 31, 2016 and March 31, 2015.

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 capital lease agreements that are subject to either fixed market interest rates set at the time of issue or floating rates determined by on-going 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 agreements, designated as fair value hedges, to manage the mix of fixed and floating rate debt.

Forward starting swaps

During the fourth quarter of 2014, the Company entered into forward starting floating-to-fixed interest rate swap agreements (“forward starting swaps”) totaling a notional U.S. $1.4 billion to fix the benchmark rate on cash flows associated with highly probable forecasted issuances of long-term notes. The effective portion of changes in fair value on the forward starting swaps is recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the probable forecasted notes are issued. Subsequent to the notes issuance, amounts in “Accumulated other comprehensive loss” are reclassified to “Net interest expense”.

During the first quarter of 2015, the Company settled a notional U.S. $700 million of forward starting swaps related to the U.S. $700 million 2.900% 10-year notes issued in the same period. The fair value of these derivative instruments was a loss of U.S. $50 million ($63 million) at the time of settlement. The effective portion of changes in fair value on the forward starting swaps of U.S. $48 million ($60 million), was recorded in “Accumulated other comprehensive loss”, and is amortized to “Net interest expense” over the term of the underlying hedged notes. During the three months ended March 31, 2016, a loss of $1 million related to these previously settled derivatives has been amortized to “Net interest expense” (three months ended March 31, 2015 - loss of $1 million). The Company expects that during the next 12 months $6 million of losses will be amortized to “Net interest expense”. The ineffective portion of U.S. $2 million ($2 million) was recorded immediately in income as “Net interest expense” during the first quarter of 2015.

During the third quarter of 2015, the Company de-designated the hedging relationship for U.S. $700 million of forward starting swaps related to a portion of the U.S. $900 million 6.125% 100-year notes issued. The Company did not cash settle these swaps and therefore recorded a non-cash loss of U.S. $36 million ($47 million) at the time of de-designation. The effective portion of changes in fair value of the de-designated forward starting swaps of U.S. $36 million ($47 million) was recorded in “Accumulated other comprehensive loss” and is amortized to “Net interest expense” over the first 10 years as the underlying interest expense payments, which are hedged, of the U.S. $900 million notes are made. During the three months ended March 31, 2016, a loss of $1 million related to these previously de-designated derivatives has been amortized to “Net interest expense”. The Company expects that during the next 12 months $5 million of losses will be amortized to “Net interest expense”. There was no ineffectiveness to record upon de-designation.

During the third quarter of 2015, the Company re-designated the forward starting swaps totalling U.S. $700 million to fix the benchmark rate on cash flows associated with a highly probable forecasted issuance of long-term notes. The effective portion of changes in fair value from the re-designation date on the forward starting swaps is recorded in “Accumulated other comprehensive loss”, net of tax, as cash flow hedges until the probable forecasted notes are issued. Subsequent to the notes being issued, amounts in “Accumulated other comprehensive loss” will be amortized to “Net interest expense”.

As at March 31, 2016, the total fair value loss of $112 million derived from the remaining forward starting swaps was included in “Accounts payable and accrued liabilities” of which $65 million relates to the re-designated existing forward starting swaps. The effective portion of $63 million on the re-designated existing forward starting swaps is reflected in “Other comprehensive (loss) income” and the ineffective portion of $2 million is recorded to “Net interest expense” on the Consolidated Statements of Comprehensive Income and the Consolidated Statements of Income, respectively.

As at December 31, 2015, the total fair value loss of $60 million derived from the remaining forward starting swaps was included in "Accounts payable and accrued liabilities" of which $13 million related to the re-designated existing forward starting swaps. The effective portion of $13 million on the re-designated existing forward starting swaps was reflected in "Other comprehensive income" and the negligible ineffective portion was recorded to "Net interest expense" on the Consolidated Statements of Comprehensive Income and the Consolidated Statements of Income, respectively.