FINANCIAL INSTRUMENTS - Foreign currency exchange rate risk management (Details) - Foreign currency exchange rate risk	12 Months Ended
Dec. 31, 2017 USD ($) $ / $
Cash flow hedges \| Forward contracts
Disclosure of detailed information about hedging instruments [line items]
Notional amount	$ 2,339,000,000
Cross currency swaps \| Cash flow hedges \| Currency swap contract, term through November 2021
Disclosure of detailed information about hedging instruments [line items]
Amount	500
Exchange rate (US$/C$) \| $ / $	1.022
Cross currency swaps \| Cash flow hedges \| Currency swap contract, term through March 2038
Disclosure of detailed information about hedging instruments [line items]
Amount	550
Exchange rate (US$/C$) \| $ / $	1.170
Cross currency swaps \| US \| 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 \| US \| 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 \| 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 \| 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
Disclosure of detailed information about hedging instruments [line items]
Notional amount	$ 3,705,000,000
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
-Note Effective 2018-01-01
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-IssueDate 2017-01-01
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+ References

No definition available.

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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

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
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