Financial Instruments - Foreign Currency Exchange Rate Risk Management (Details)	12 Months Ended
Dec. 31, 2019 USD ($) $ / $
Foreign currency exchange rate risk \| Cash flow hedges \| Forward contracts
Disclosure of detailed information about hedging instruments [line items]
Notional amount	$ 3,999,000,000
USD
Disclosure of detailed information about hedging instruments [line items]
Exchange rate (US$/C$)	1.00
Cross currency swaps \| Foreign currency exchange rate risk \| Cash flow hedges \| Currency swap contract, term through November 2021
Disclosure of detailed information about hedging instruments [line items]
Amount	500,000,000
Exchange rate (US$/C$) \| $ / $	1.022
Cross currency swaps \| Foreign currency exchange rate risk \| Cash flow hedges \| Currency swap contract, term through March 2038
Disclosure of detailed information about hedging instruments [line items]
Amount	550,000,000
Exchange rate (US$/C$) \| $ / $	1.170
Cross currency swaps \| USD \| Foreign currency exchange rate risk \| Cash flow hedges \| Currency swap contract, term through November 2021
Disclosure of detailed information about hedging instruments [line items]
Interest rate	3.45%
Cross currency swaps \| USD \| Foreign currency exchange rate risk \| Cash flow hedges \| Currency swap contract, term through March 2038
Disclosure of detailed information about hedging instruments [line items]
Interest rate	6.25%
Cross currency swaps \| CAD \| Foreign currency exchange rate risk \| Cash flow hedges \| Currency swap contract, term through November 2021
Disclosure of detailed information about hedging instruments [line items]
Interest rate	3.96%
Cross currency swaps \| CAD \| Foreign currency exchange rate risk \| Cash flow hedges \| Currency swap contract, term through March 2038
Disclosure of detailed information about hedging instruments [line items]
Interest rate	5.76%
Forward contracts \| Foreign currency exchange rate risk
Disclosure of detailed information about hedging instruments [line items]
Notional amount	$ 4,564,000,000
Derivative, term of contract	90 days

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- Definition

The average exchange rate used by the entity. Exchange rate is the ratio of exchange for two currencies.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

The average rate of a hedging instrument. [Refer: Hedging instruments [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-IssueDate 2019-01-01
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+ References

No definition available.

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- Definition

The nominal amount of a hedging instrument. [Refer: Hedging instruments [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

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+ References

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