Retirement Benefit Obligations - Summary of Reconciliation of Actuarial Value of Liabilities (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of defined benefit plans [Line Items]
Current service cost	€ (43)	€ (43)	€ (40)
Past service credit (net)	(18)	(13)	(17)
Interest cost on scheme liabilities	(77)	(65)	(55)
Defined pension liabilities [member]
Disclosure of defined benefit plans [Line Items]
Beginning balance	(3,337)	(2,999)
Current service cost	(60)	(64)
Past service credit (net)	18	17
Interest cost on scheme liabilities	(81)	(69)
Arising on acquisition (note 32)	(4)	(452)
Disposals	636	6
Remeasurement adjustments - experience variations	33	1
Remeasurement adjustments - actuarial (loss)/gain from changes in financial assumptions	(384)	120
Remeasurement adjustments - actuarial (loss)/gain from changes in demographic assumptions	18	26
Contributions paid by plan participants	(13)	(14)
Benefit and settlement payments	139	130
Translation adjustment	(74)	(39)
Ending balance	€ (3,109)	€ (3,337)	€ (2,999)

Gain loss on remeasurement of experience variations net defined liability asset.

No definition available.

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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from disposals. [Refer: Business combinations [member]; Net defined benefit liability (asset)]

+ References

No definition available.

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- Definition

Interest expense, net defined benefit liability (asset).

+ References

No definition available.

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- Definition

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions that result in remeasurements of the net defined benefit liability (asset). Demographic assumptions deal with matters such as: (a) mortality; (b) rates of employee turnover, disability and early retirement; (c) the proportion of plan members with dependants who will be eligible for benefits; (d) the proportion of plan members who will select each form of payment option available under the plan terms; and (e) claim rates under medical plans. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2019-01-01
-Paragraph 141
-Subparagraph c
-Clause ii
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- Definition

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions that result in remeasurements of the net defined benefit liability (asset). Financial assumptions deal with items such as: (a) the discount rate; (b) benefit levels, excluding any cost of the benefits to be met by employees, and future salary; (c) in the case of medical benefits, future medical costs, including claim handling costs (ie the costs that will be incurred in processing and resolving claims, including legal and adjuster's fees); and (d) taxes payable by the plan on contributions relating to service before the reporting date or on benefits resulting from that service. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from contributions to a defined benefit plan by plan participants. [Refer: Net defined benefit liability (asset); Defined benefit plans [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from employee service in the current period. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from business combinations and disposals. [Refer: Business combinations [member]; Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2019-01-01
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- Definition

The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2019-01-01
-Paragraph 140
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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from past service cost. Past service cost is the change in the present value of the defined benefit obligation for employee service in prior periods, resulting from a plan amendment (the introduction or withdrawal of, or changes to, a defined benefit plan) or a curtailment (a significant reduction by the entity in the number of employees covered by a plan). [Refer: Net defined benefit liability (asset); Defined benefit plans [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2019-01-01
-Paragraph 141
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- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan. [Refer: Net defined benefit liability (asset)]

+ References

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