Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail) - EUR (€) € in Millions	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and cash equivalents [abstract]
Cash in bank and on hand	€ 166	€ 269
Total Cash and cash equivalents	€ 166	€ 269	€ 347

The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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