Investments Accounted for Under Equity Method - Summary of Share of Joint Ventures (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of joint ventures [line items]
Group share of joint venture's net assets	€ 1	€ 1	€ 16
Group share of joint venture's profit / (loss)	€ (33)	€ (29)	€ (14)
Constellium-Bowling Green [member]
Disclosure of joint ventures [line items]
% interest	51.00%	51.00%
Group share of joint venture's net assets	€ (49)	€ (14)
Group share of joint venture's profit / (loss)	€ (33)	€ (29)
Rhenaroll S.A. [member]
Disclosure of joint ventures [line items]
% interest	49.85%	49.85%
Group share of joint venture's net assets	€ 1	€ 1
Group share [member]
Disclosure of joint ventures [line items]
Group share of joint venture's net assets	(48)	(13)
Group share of joint venture's profit / (loss)	(33)	(29)
Reclassified to non-current other financial assets [member]
Disclosure of joint ventures [line items]
Group share of joint venture's net assets	€ 49	€ 14

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.

No definition available.

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The amount of investments accounted for using the equity method. The equity method is a method of accounting whereby the investment is initially recognised at cost and adjusted thereafter for the post-acquisition change in the investor's share of net assets of the investee. The investor's profit or loss includes its share of the profit or loss of the investee. The investor's other comprehensive income includes its share of the other comprehensive income of the investee. [Refer: At cost [member]]

+ References

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The proportion of ownership interest in a joint venture attributable to the entity. [Refer: Joint ventures [member]]

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- Definition

The entity's share of the profit (loss) of joint ventures accounted for using the equity method. [Refer: Investments accounted for using equity method; Joint ventures [member]; Profit (loss)]

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