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Other Gains / (Losses)-Net - Summary of Other Gains/(Losses) Net (Parenthetical) (Detail) - EUR (€) € in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Analysis of other gains losses [line items]
Gains / (Losses) on pension plans amendments		€ 36	€ 20
Cash payment received on acquisition				€ 21
Gain net of costs on acquisition				€ 20
Disposal of leased assets [member] | Novelis [member]
Analysis of other gains losses [line items]
Sale of assets	€ 200
Net gain on sale of assets	€ 190

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- Definition

Acquisition purchase price adjustment.

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- Definition

Analysis of other gains losses [line items]

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- Definition

Cash payment received upon acquisition.

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- Definition

Gains (losses) on pension plan amendments.

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- Definition

The gains (losses) on disposals of property, plant and equipment. [Refer: Property, plant and equipment]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The cash inflow from the disposal of property, plant and equipment, intangible assets other than goodwill, investment property and other non-current assets. [Refer: Intangible assets other than goodwill; Investment property; Other non-current assets; Property, plant and equipment]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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