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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%

X

- Definition

Borrowings nominal interest rate.

+ References

No definition available.

+ Details

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X

- Definition

Deferred loan origination fees and costs.

+ References

No definition available.

+ Details

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X

- Definition

Line of credit facility amount.

+ References

No definition available.

+ Details

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X

- Definition

Line of credit facility committed accordion amount.

+ References

No definition available.

+ Details

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X

- Definition

Secured revolving credit facility.

+ References

No definition available.

+ Details

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

The amount of notes and debentures issued by the entity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2017-03-09

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- Details

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- Details

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