v3.19.2
financial instruments - Fair Values Derivatives (Details)
 6 Months Ended 12 Months Ended
Jun. 30, 2019
CAD ($)
$ / $
Dec. 31, 2018
CAD ($)
$ / $
Disclosure of detailed information about financial instruments    
Current Assets, Fair value and carrying value $ 10,000,000 $ 49,000,000
Current Liabilities, Fair value and carrying value $ 5,000,000 $ 9,000,000
Derivatives | Cash flow hedging item (HFH)    
Disclosure of detailed information about financial instruments    
Hedge ratio 100.00% 100.00%
Current Asset derivatives    
Disclosure of detailed information about financial instruments    
Current Assets, Fair value and carrying value $ 10,000,000 $ 49,000,000
Current Asset derivatives | Currency risk related to purchases | Cash flow hedging item (HFH) | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2020 2019
Current Assets, Notional amount $ 155,000,000 $ 414,000,000
Current Assets, Fair value and carrying value $ 2,000,000 $ 25,000,000
Rate | $ / $ 1.29 1.28
Current Asset derivatives | Currency risk related to revenues | HFT | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2019 2019
Current Assets, Notional amount $ 53,000,000 $ 74,000,000
Current Assets, Fair value and carrying value $ 2,000,000 $ 1,000,000
Rate | $ / $ 1.31 1.36
Current Asset derivatives | Other market risk | Cash flow hedging item (HFH)    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2019 2019
Current Assets, Notional amount $ 66,000,000 $ 63,000,000
Current Assets, Fair value and carrying value 6,000,000 2,000,000
Price $ 45.53 $ 45.46
Current Asset derivatives | Currency risk related to long-term debt | Cash flow hedging item (HFH) | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date - 2019
Current Assets, Notional amount   $ 761,000,000
Current Assets, Fair value and carrying value   $ 21,000,000
Rate | $ / $   1.33
Other Long-Term Asset derivatives    
Disclosure of detailed information about financial instruments    
Other Long-Term Assets, Fair value and carrying value $ 2,000,000 $ 54,000,000
Other Long-Term Asset derivatives | Other market risk | Cash flow hedging item (HFH)    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2020  
Price $ 48.71  
Other Long-Term Assets, Notional amount 67,000,000  
Other Long-Term Assets, Fair value and carrying value $ 2,000,000  
Other Long-Term Asset derivatives | Currency risk related to long-term debt | Cash flow hedging item (HFH) | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date - 2048
Rate | $ / $   1.28
Other Long-Term Assets, Notional amount   $ 3,134,000,000
Other Long-Term Assets, Fair value and carrying value   54,000,000
Current Liabilities derivatives    
Disclosure of detailed information about financial instruments    
Current Liabilities, Fair value and carrying value $ 5,000,000 $ 9,000,000
Current Liabilities derivatives | Currency risk related to purchases | Cash flow hedging item (HFH) | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2020 2019
Rate | $ / $ 1.32 1.36
Current Liabilities, Notional amount $ 287,000,000 $ 11,000,000
Current Liabilities, Fair value and carrying value $ 3,000,000  
Current Liabilities derivatives | Currency risk related to revenues | HFT | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date - 2019
Rate   1.36
Current Liabilities, Notional amount   $ 18,000,000
Current Liabilities derivatives | Other market risk | Cash flow hedging item (HFH)    
Disclosure of detailed information about financial instruments    
Maximum maturity date - 2019
Rate | $ / $   47.39
Current Liabilities, Notional amount   $ 2,000,000
Current Liabilities derivatives | Currency risk related to long-term debt | Cash flow hedging item (HFH) | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2019 -
Current Assets, Notional amount $ 296,000,000  
Current Assets, Fair value and carrying value $ 2,000,000  
Rate | $ / $ 1.31  
Current Liabilities derivatives | Interest rate risk | Cash flow hedging item (HFH) | GOC 2.14% 10-year term note    
Disclosure of detailed information about financial instruments    
Interest rate on borrowings   2.40%
Debt instrument term   10 years
Current Liabilities derivatives | Interest rate risk | Cash flow hedging item (HFH) | GOC 2.40% 10-year term note    
Disclosure of detailed information about financial instruments    
Maximum maturity date - 2019
Current Liabilities, Notional amount   $ 250,000,000
Current Liabilities, Fair value and carrying value   $ 9,000,000
Current Liabilities derivatives | Interest rate risk | Cash flow hedging item (HFH) | 2.64% non-fixed rate credit facility    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2020 2019
Current Assets, Notional amount $ 8,000,000 $ 8,000,000
Rate | $ / $ 2.64 2.64
Other Long-Term Liabilities derivatives    
Disclosure of detailed information about financial instruments    
Other Long-Term Liabilities, Fair value and carrying value $ 94,000,000 $ 6,000,000
Other Long-Term Liabilities derivatives | Other market risk | Cash flow hedging item (HFH)    
Disclosure of detailed information about financial instruments    
Maximum maturity date - 2020
Rate | $ / $   48.71
Other Long-Term Liabilities, Notional amount   $ 67,000,000
Other Long-Term Liabilities, Fair value and carrying value   $ 3,000,000
Other Long-Term Liabilities derivatives | Currency risk related to long-term debt | Cash flow hedging item (HFH) | U.S. Dollars    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2049 2027
Rate | $ / $ 1.30 1.33
Other Long-Term Liabilities, Notional amount $ 5,614,000,000 $ 991,000,000
Other Long-Term Liabilities, Fair value and carrying value 90,000,000 2,000,000
Spread included in fair value of derivative instruments $ 36,000,000 $ 29,000,000
Other Long-Term Liabilities derivatives | Interest rate risk | Cash flow hedging item (HFH) | 2.64% non-fixed rate credit facility    
Disclosure of detailed information about financial instruments    
Maximum maturity date 2022 2022
Rate | $ / $ 2.64 2.64
Other Long-Term Liabilities, Notional amount $ 135,000,000 $ 145,000,000
Other Long-Term Liabilities, Fair value and carrying value $ 4,000,000 $ 1,000,000