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Borrowings - Summary of Borrowings (Parenthetical) (Detail) € in Millions |  |  | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Nov. 09, 2017 EUR (€) | Feb. 16, 2017 EUR (€) | Dec. 31, 2017 | Nov. 09, 2017 USD ($) | Jun. 21, 2017 USD ($) | Apr. 21, 2017 EUR (€) | Feb. 16, 2017 USD ($)
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Principle amount |  |  |  |  |  |  | $ 650,000,000
Nominal rate |  | 6.625% |  |  |  |  |
Deferred arrangement fees | € | € 15 | € 14 |  |  |  |  |
Pan US ABL facility (due 2022) [member] |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Credit facility |  |  |  |  | $ 300,000,000 |  |
Credit facility committed accordion |  |  |  |  | $ 200,000,000 |  |
French entities [member] |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Secured revolving credit facility | € |  |  |  |  |  | € 100 |
Constellium N.V. USD Senior Unsecured Notes (Issued November 2017, due 2026) [member] |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Principle amount |  |  |  | $ 500,000,000 |  |  |
Nominal rate | 5.875% |  | 5.88% |  |  |  |
Constellium N.V. EURO Senior Unsecured Notes (Issued November 2017, due 2026) [member] |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Principle amount | € | € 400 |  |  |  |  |  |
Nominal rate | 4.25% |  | 4.25% |  |  |  |

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