XML 171 R134.htm IDEA: XBRL DOCUMENT v3.8.0.1

Financial Risk Management - Summary of Nominal Value of Currency Derivatives (Detail) - Currency risk [member] EUR_ in Millions	Dec. 31, 2017 EUR_
Forward derivatives sales - USD/EUR [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Maturity Period	2018-2023
Forward derivatives sales - EUR/CHF [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Maturity Period	2018-2022
forward derivatives sales - Other currencies [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Maturity Period	2018-2020
Forward derivatives purchases - USD/EUR [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Maturity Period	2018-2022
Forward derivatives purchases - EUR/CHF [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Maturity Period	2018-2022
Forward derivatives purchases - EUR/CZK [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Maturity Period	2018-2019
Forward derivatives purchases - Other currencies [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Maturity Period	2018
Less than 1 year [member] | Forward derivatives sales - USD/EUR [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	387
Less than 1 year [member] | Forward derivatives sales - EUR/CHF [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	49
Less than 1 year [member] | forward derivatives sales - Other currencies [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	16
Less than 1 year [member] | Forward derivatives purchases - USD/EUR [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	395
Less than 1 year [member] | Forward derivatives purchases - EUR/CHF [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	103
Less than 1 year [member] | Forward derivatives purchases - EUR/CZK [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	63
Less than 1 year [member] | Forward derivatives purchases - Other currencies [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	1
Over 1 year [member] | Forward derivatives sales - USD/EUR [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	376
Over 1 year [member] | Forward derivatives sales - EUR/CHF [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	19
Over 1 year [member] | forward derivatives sales - Other currencies [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	2
Over 1 year [member] | Forward derivatives purchases - USD/EUR [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	90
Over 1 year [member] | Forward derivatives purchases - EUR/CHF [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	35
Over 1 year [member] | Forward derivatives purchases - EUR/CZK [member]
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal value	62

X

- Definition

Derivative instrument maturity period.

+ References

No definition available.

+ Details

Name:	cstm_DerivativeInstrumentMaturityPeriod
Namespace Prefix:	cstm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- 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.

+ Details

Name:	ifrs-full_DisclosureOfInformationAboutTermsAndConditionsOfHedgingInstrumentsAndHowTheyAffectFutureCashFlowsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The nominal amount of a hedging instrument. [Refer: Hedging instruments [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 23B
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_23B_a&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2017-01-01
-Paragraph 24A
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_24A_d&doctype=Standard
-URIDate 2017-03-09

+ Details

Name:	ifrs-full_NominalAmountOfHedgingInstrument
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	ifrs-full_TypesOfRisksAxis=ifrs-full_CurrencyRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_HedgingInstrumentsAxis=cstm_UsdEurForwardDerivativesSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_HedgingInstrumentsAxis=cstm_EurChfForwardDerivativesSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_HedgingInstrumentsAxis=cstm_OtherCurrenciesForwardDerivativesSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_HedgingInstrumentsAxis=cstm_UsdEurForwardDerivativesPurchasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_HedgingInstrumentsAxis=cstm_EurChfForwardDerivativesPurchasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_HedgingInstrumentsAxis=cstm_ForwardDerivativesPurchasesEurCzkMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_HedgingInstrumentsAxis=cstm_OtherCurrenciesForwardDerivativesPurchasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_MaturityAxis=ifrs-full_NotLaterThanOneYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_MaturityAxis=ifrs-full_LaterThanOneYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: