Share-based Payment Expense - Summary of Movement and Options Outstanding Under Share Option Schemes (Parenthetical) (Detail) - Share Option Schemes Excluding Savings Related Share Option Schemes [member]	12 Months Ended
	Dec. 31, 2019 yr € / shares	Dec. 31, 2018 € / shares	Dec. 31, 2017 € / shares
Disclosure Of Share Based Compensation Expense [line items]
Weighted average share price | € / shares	€ 29.10	€ 27.90	€ 32.24
Description of option Life share options granted | yr	10