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Intangible assets - Summary of intangible assets (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Intangible assets | $ 2,779 | $ 3,119 | $ 3,279
Disposals, transfers and other movements | $ (134) | $ 36 |
Quebec smelters [member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Fair value less costs of disposal, post-tax discount rate | 6.80% | 6.70% |
Description of recoverable amount of asset is fair value less costs of disposal or value in use | the Quebec smelters CGU. The Quebec smelters CGU was tested for impairment by reference to FVLCD using discounted cash flows, which is in line with the policy set out in note 1(i). The recoverable amount of the Quebec smelters is classified as level 3 under the fair value hierarchy |  |
Description of level of fair value hierarchy within which fair value measurement is categorized | level 3 |  |
Water rights [member] | Quebec smelters [member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Intangible assets | $ 1,684 |  |
Trademarks [member] | Bottom of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | 14 years |  |
Trademarks [member] | Top of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | 20 years |  |
Patented and non-patented technology [member] | Bottom of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | ten years |  |
Patented and non-patented technology [member] | Top of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | 20 years |  |
Power contracts water rights [member] | Bottom of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | two years |  |
Power contracts water rights [member] | Top of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | 45 years |  |
Other purchase and customer contracts [member] | Bottom of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | five years |  |
Other purchase and customer contracts [member] | Top of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | 15 years |  |
Computer software [Member] | Bottom of range [Member] | Internally generated [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | two years |  |
Computer software [Member] | Top of range [Member] | Internally generated [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | five years |  |
Other intangible assets [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Intangible assets | $ 505 | $ 463 | 387
Disposals, transfers and other movements | $ 103 | 79 |
Other intangible assets [Member] | Bottom of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | two years |  |
Other intangible assets [Member] | Top of range [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Finite life intangible assets, useful lives | 20 years |  |
Exploration and evaluation [member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Intangible assets | $ 233 | 393 | $ 711
Disposals, transfers and other movements | $ (225) | (45) |
Exploration and evaluation [member] | Kemano Tunnel Project [Member] |  |  |
Disclosure of detailed information about intangible assets [Line Items] |  |  |
Disposals, transfers and other movements |  | $ 34 |

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