Share Capital and Reserves - Summary of Share Premium (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Share Premium [Abstract]
At 1 January	€ 6,237	€ 6,021
Premium arising on shares issued	180	216
At 31 December	€ 6,417	€ 6,237

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 2016-01-13
-Paragraph 78
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_78_e&doctype=Standard
-URIDate 2016-03-31

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