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Finance Costs-Net - Summary of Finance Costs - Net (Parenthetical) (Detail) - EUR (€) € in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Analysis of income and expense [line items] |  |  |  |
Other finance expense | € 3 | € 6 | € 13 | € 8
Capitalisation rate |  |  | 6.00% | 7.00%
Constellium N.V. Senior Notes [member] |  |  |  |
Analysis of income and expense [line items] |  |  |  |
Interest expense on debt instrument |  |  | € 56 | € 69
Muscle Shoals' Senior Notes [member] |  |  |  |
Analysis of income and expense [line items] |  |  |  |
Interest expense on debt instrument |  |  |  | 7
Revolving Credit Facility 1 [member] |  |  |  |
Analysis of income and expense [line items] |  |  |  |
Interest expense on debt instrument |  |  |  | € 3
Pan US ABL Facility [member] |  |  |  |
Analysis of income and expense [line items] |  |  |  |
Interest expense on debt instrument |  |  | 2 |
Constellium UACJ loan modification [member] |  |  |  |
Analysis of income and expense [line items] |  |  |  |
Other finance expense |  |  | € 6 |

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