XML 127 R90.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Income Tax - Summary of Income Tax Reconciliation Using Composite Statutory Income Tax Rate Applicable by Tax Jurisdictions (Detail) - EUR (€) € in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure Of Income Tax Expense [Abstract] |  |  |
Income / (Loss) before income tax | € 49 | € 65 | € (584)
Composite statutory income tax rate applicable by tax jurisdiction | 31.90% | 24.90% | 38.20%
Income tax (expense) / benefit calculated at composite statutory tax rate applicable by tax jurisdictions | € (16) | € (16) | € 223
Tax effect of: |  |  |
Changes in recognized and unrecognized deferred tax assets | (61) | (45) | (177)
Change in tax rate | (11) | (6) |
Other | 8 | (2) | (14)
Income tax (expense) / benefit | € (80) | € (69) | € 32
Effective income tax rate | 163.00% | 106.00% | 5.00%

X
- Definition Disclosure of income tax expense. + References No definition available. + Details
Name: | cstm_DisclosureOfIncomeTaxExpenseAbstract
Namespace Prefix: | cstm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Adjustments for deferred tax expense to reconcile profit (loss) to net cash flow from (used in) operating activities. [Refer: Deferred tax expense (income); Profit (loss)] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 7 -IssueDate 2017-01-01 -Paragraph 20 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2017-03-01&anchor=para_20&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_AdjustmentsForDeferredTaxExpense
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The applicable income tax rate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_ii&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_ApplicableTaxRate
Namespace Prefix: | ifrs-full_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The tax expense (income) divided by the accounting profit. [Refer: Accounting profit] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_ii&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_AverageEffectiveTaxRate
Namespace Prefix: | ifrs-full_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The aggregate amount included in the determination of profit (loss) for the period in respect of current tax and deferred tax that relate to continuing operations. [Refer: Continuing operations [member]; Current tax expense (income); Deferred tax expense (income)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 26 -IssueDate 2017-01-01 -Paragraph 35 -Subparagraph b -Clause viii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=26&date=2017-03-01&anchor=para_35_b_viii&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2017-01-01 -Paragraph 23 -Subparagraph h -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=8&date=2017-03-01&anchor=para_23_h&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 79 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_79&doctype=Standard -URIDate 2017-03-09 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_i&doctype=Standard -URIDate 2017-03-09 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 82 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_82_d&doctype=Standard -URIDate 2017-03-09 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_ii&doctype=Standard -URIDate 2017-03-09 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2017-01-01 -Paragraph B13 -Subparagraph g -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_B13_g&doctype=Appendix&seq=2 -URIDate 2017-03-09 + Details
Name: | ifrs-full_IncomeTaxExpenseContinuingOperations
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that the entity does not separately disclose in the same statement or note. [Refer: Accounting profit; Applicable tax rate] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_i&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_OtherTaxEffectsForReconciliationBetweenAccountingProfitAndTaxExpenseIncome
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The profit (loss) from continuing operations before tax expense or income. [Refer: Profit (loss)] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 8 -IssueDate 2017-01-01 -Paragraph 28 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=8&date=2017-03-01&anchor=para_28_b&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 8 -IssueDate 2017-01-01 -Paragraph 23 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=8&date=2017-03-01&anchor=para_23&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 103 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_103&doctype=Standard -URIDate 2017-03-09 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 102 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_102&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_ProfitLossBeforeTax
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | ifrs-full_ReconciliationOfAccountingProfitMultipliedByApplicableTaxRatesAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to changes in the tax rate. [Refer: Accounting profit] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_i&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_TaxEffectFromChangeInTaxRate
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The product of the accounting profit multiplied by the applicable tax rate(s). [Refer: Accounting profit; Applicable tax rate] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2017-01-01 -Paragraph 81 -Subparagraph c -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2017-03-01&anchor=para_81_c_i&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_TaxExpenseIncomeAtApplicableTaxRate
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration