The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Nominal or face amount used to calculate payments on the derivative liability.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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The amount of net gains or losses on interest rate cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

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Financial Instruments (Details) $ in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 CAD ($)	Jun. 30, 2017 CAD ($)	Jun. 30, 2018 CAD ($)	Jun. 30, 2017 CAD ($)	Jun. 30, 2018 USD ($)
U.S. $500 million 4.000% 10-year Notes
Schedule of Investments [Line Items]
Debt Instrument, Face Amount					$ 500
Debt Instrument, Interest Rate	4.00%		4.00%		4.00%
Debt Instrument, Term	10 years
Forward Starting Swaps [Member]
Schedule of Investments [Line Items]
Floating-to-fixed interest rate swaps, Notional amount					$ 500
Fair value loss	$ (24)		$ (24)		$ (19)
Gain (Loss) on Derivative, Net	12	$ (14)	31	$ (12)
Forward Starting Swaps [Member] \| Net Interest Expense [Member]
Schedule of Investments [Line Items]
Derivative losses amortized to net interest expense	2	2	5	5
Derivative losses expected to be amortized to net interest expense			(9)
Net Investment Hedging [Member]
Schedule of Investments [Line Items]
Gain (Loss) on Derivative, Net	$ (122)	$ 116	$ (273)	$ 162