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Borrowings - Summary of Composition of Carrying Amounts of Total Borrowings (Detail) - EUR (€) € in Millions	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of detailed information about borrowings [line items]
Total borrowings	€ 2,184	€ 2,127	€ 2,468
U.S. Dollar [member]
Disclosure of detailed information about borrowings [line items]
Total borrowings	1,442	1,387
Euro [member]
Disclosure of detailed information about borrowings [line items]
Total borrowings	722	720
Other currencies [member]
Disclosure of detailed information about borrowings [line items]
Total borrowings	€ 20	€ 20

X

- Definition

The amount of outstanding funds that the entity is obligated to repay.

+ References

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

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