Retirement Benefit Obligations - Summary of Retirement Benefit Expense in Consolidated Income Statement (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Defined Benefit Plans And Defined Contribution Expenses Recognized In Income Statement [abstract]
Total defined contribution expense	€ 259	€ 225	€ 228
Total defined benefit expense/(credit)	45	43	36
Total expense in Consolidated Income Statement	€ 304	€ 268	€ 264

The amount of post-employment benefit expense relating to defined contribution plans. Defined contribution plans are post-employment benefit plans under which an entity pays fixed contributions into a separate entity (a fund) and will have no legal or constructive obligation to pay further contributions if the fund does not hold sufficient assets to pay all employee benefits relating to employee service in the current and prior periods.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2019-01-01
-Paragraph 53
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_53&doctype=Standard
-URIDate 2019-03-27

Name:	ifrs-full_PostemploymentBenefitExpenseDefinedContributionPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration