Share-based Payment Expense - Summary of Assumptions of Fair Value Options (Detail)	12 Months Ended
Dec. 31, 2017 EUR (€) yr	Dec. 31, 2016 EUR (€) yr	Dec. 31, 2015 EUR (€) yr
2010 Savings-related share option - 3 year [Member]
Disclosure Of Share Based Compensation Expense [Line Items]
Weighted average exercise price (€)	€ 27.86	€ 20.83	€ 21.12
Risk-free interest rate (%)	(0.72%)	(0.48%)	(0.22%)
Expected dividend payments over the expected life (€)	€ 2.07	€ 1.95	€ 1.91
Expected volatility (%)	20.90%	21.80%	21.60%
Expected life in years \| yr	3	3	3
2010 Savings-related share option - 5 year [Member]
Disclosure Of Share Based Compensation Expense [Line Items]
Weighted average exercise price (€)	€ 27.86	€ 20.83	€ 21.12
Risk-free interest rate (%)	(0.45%)	(0.33%)	(0.09%)
Expected dividend payments over the expected life (€)	€ 3.55	€ 3.32	€ 3.25
Expected volatility (%)	20.60%	22.90%	27.80%
Expected life in years \| yr	5	5	5

Disclosure of share-based compensation expense.

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- Definition

The expected volatility of the share price used to calculate the fair value of the share options granted. Expected volatility is a measure of the amount by which a price is expected to fluctuate during a period. The measure of volatility used in option pricing models is the annualised standard deviation of the continuously compounded rates of return on the share over a period of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2016-01-13
-Paragraph 47
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2016-03-30&anchor=para_47_a_i&doctype=Standard
-URIDate 2016-03-31

+ Details

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- Definition

The option life of share options granted.

+ References

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- Definition

The implied yield currently available on zero-coupon government issues of the country in whose currency the exercise price for share options granted is expressed, with a remaining term equal to the expected term of the option being valued (based on the option's remaining contractual life and taking into account the effects of expected early exercise). [Refer: Government [member]]

+ References

+ Details

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- Definition

The amount of an expected dividend used to calculate the fair value of share options granted.

+ References

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- Definition

The weighted average exercise price of share options granted in a share-based payment arrangement. [Refer: Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2016-01-13
-Paragraph 45
-Subparagraph b
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2016-03-30&anchor=para_45_b_ii&doctype=Standard
-URIDate 2016-03-31

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