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Financial Risk Management - Additional Information (Detail) € in Millions, $ in Millions | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2017 EUR (€) | Dec. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 EUR (€) | Dec. 31, 2015 EUR (€) | Dec. 31, 2014 EUR (€)
Disclosure of credit risk [line items] |  |  |  |  |  |
Percentage borrowings denominated in fixed rate | 96.00% |  | 96.00% |  |  |
Percentage of trade account receivables insured | 89.00% |  | 89.00% |  |  |
Liquidity value | € 531 |  |  |  |  |
Cash and cash equivalents | 269 |  |  | € 347 | € 472 | € 991
Undrawn facilities | 262 |  |  |  |  |
Revolving credit facilities outstanding | 207 |  |  |  |  |
Derivative classified as cash flow hedge [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Nominal amount hedging instrument | $ |  |  | $ 484 |  |  |
Forward purchase contracts versus EURO [Member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Net position hedges related to loans and deposits | $ |  | $ 436 |  |  |  |
Forward purchase contracts [member] | Cross currency swaps [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Net position hedges related to loans and deposits | $ |  | 870 |  |  |  |
Forward sale contracts [member] | Foreign exchange forward contracts [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Net position hedges related to loans and deposits | $ |  | 294 |  |  |  |
Forward sale contracts [member] | Cross currency swaps [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Net position hedges related to loans and deposits | $ |  | $ 140 |  |  |  |
Pan US ABL facility (due 2022) [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Borrowing base | $ |  |  | $ 249 |  |  |
Secured inventory based facility (due 2019) [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Borrowing base | 71 |  |  |  |  |
10% increase or decrease in the market price [member] | Aluminium [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Impact of increase or decrease in market price in gain or loss from derivatives | € 35 |  |  |  |  |
Bottom of range [member] | Derivative classified as cash flow hedge [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Maturity period | 2018 | 2018 |  |  |  |
Top of range [member] | Derivative classified as cash flow hedge [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Maturity period | 2022 | 2022 |  |  |  |
Top of range [member] | 50 basis point increase or decrease in the LIBOR or EURIBOR interest rates [member] |  |  |  |  |  |
Disclosure of credit risk [line items] |  |  |  |  |  |
Impact of increase or decrease in interest rate in income/loss before income tax | € 1 |  |  |  |  |

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