Share Capital and Reserves - Summary of Share Premium (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Share Premium [abstract]
At 1 January	€ 6,534	€ 6,417
Premium arising on shares issued		117
At 31 December	€ 6,534	€ 6,534

The amount received or receivable from the issuance of the entity's shares in excess of nominal value.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 78
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_78_e&doctype=Standard
-URIDate 2019-03-27

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant