Pensions and Other Post-employment Benefit Obligations - Details of Movement in Net Defined Benefit Obligations (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Disclosure of changes in financial position [line items]
Beginning balance	€ 735	€ 701
Closing balance	664	735
Consolidated Income Statement [member]
Disclosure of changes in financial position [line items]
Current service cost	24	26
Interest cost / (income)	18	21
Past service cost	(20)	1
Immediate recognition of gains/losses arising over the period		1
Administration expenses	2	2
Statement of Comprehensive Income (Loss) [member]
Disclosure of changes in financial position [line items]
- actual return less interest on plan assets	(36)	(14)
- changes in financial assumptions	37	34
- changes in demographic assumptions	(1)	(1)
- experience (gains)/losses		(3)
Effects of changes in foreign exchange rates	(48)	12
Consolidated Statement of Cash Flows [member]
Disclosure of changes in financial position [line items]
Benefits paid	(23)	(22)
Contributions by the Group	(24)	(26)
Other [member]
Disclosure of changes in financial position [line items]
Transfer		3
Defined benefit obligations [member]
Disclosure of changes in financial position [line items]
Beginning balance	1,126	1,063
Closing balance	1,051	1,126
Defined benefit obligations [member] \| Consolidated Income Statement [member]
Disclosure of changes in financial position [line items]
Current service cost	24	26
Interest cost / (income)	27	31
Past service cost	(20)	1
Immediate recognition of gains/losses arising over the period		1
Defined benefit obligations [member] \| Statement of Comprehensive Income (Loss) [member]
Disclosure of changes in financial position [line items]
- changes in financial assumptions	37	34
- changes in demographic assumptions	(1)	(1)
- experience (gains)/losses		(3)
Effects of changes in foreign exchange rates	(90)	20
Defined benefit obligations [member] \| Consolidated Statement of Cash Flows [member]
Disclosure of changes in financial position [line items]
Benefits paid	(56)	(54)
Contributions by the plan participants	4	5
Defined benefit obligations [member] \| Other [member]
Disclosure of changes in financial position [line items]
Transfer		3
Defined benefit obligations [member] \| Pension benefits [member]
Disclosure of changes in financial position [line items]
Beginning balance	853	802
Closing balance	801	853
Defined benefit obligations [member] \| Pension benefits [member] \| Consolidated Income Statement [member]
Disclosure of changes in financial position [line items]
Current service cost	18	20
Interest cost / (income)	18	21
Past service cost	(16)
Defined benefit obligations [member] \| Pension benefits [member] \| Statement of Comprehensive Income (Loss) [member]
Disclosure of changes in financial position [line items]
- changes in financial assumptions	23	28
- changes in demographic assumptions		2
- experience (gains)/losses		1
Effects of changes in foreign exchange rates	(61)	12
Defined benefit obligations [member] \| Pension benefits [member] \| Consolidated Statement of Cash Flows [member]
Disclosure of changes in financial position [line items]
Benefits paid	(38)	(37)
Contributions by the plan participants	4	4
Defined benefit obligations [member] \| Other benefits [member]
Disclosure of changes in financial position [line items]
Beginning balance	273	261
Closing balance	250	273
Defined benefit obligations [member] \| Other benefits [member] \| Consolidated Income Statement [member]
Disclosure of changes in financial position [line items]
Current service cost	6	6
Interest cost / (income)	9	10
Past service cost	(4)	1
Immediate recognition of gains/losses arising over the period		1
Defined benefit obligations [member] \| Other benefits [member] \| Statement of Comprehensive Income (Loss) [member]
Disclosure of changes in financial position [line items]
- changes in financial assumptions	14	6
- changes in demographic assumptions	(1)	(3)
- experience (gains)/losses		(4)
Effects of changes in foreign exchange rates	(29)	8
Defined benefit obligations [member] \| Other benefits [member] \| Consolidated Statement of Cash Flows [member]
Disclosure of changes in financial position [line items]
Benefits paid	(18)	(17)
Contributions by the plan participants		1
Defined benefit obligations [member] \| Other benefits [member] \| Other [member]
Disclosure of changes in financial position [line items]
Transfer		3
Plan Assets [member]
Disclosure of changes in financial position [line items]
Beginning balance	(391)	(362)
Closing balance	(387)	(391)
Plan Assets [member] \| Consolidated Income Statement [member]
Disclosure of changes in financial position [line items]
Interest cost / (income)	(9)	(10)
Administration expenses	2	2
Plan Assets [member] \| Statement of Comprehensive Income (Loss) [member]
Disclosure of changes in financial position [line items]
- actual return less interest on plan assets	(36)	(14)
Effects of changes in foreign exchange rates	42	(8)
Plan Assets [member] \| Consolidated Statement of Cash Flows [member]
Disclosure of changes in financial position [line items]
Benefits paid	33	32
Contributions by the Group	(24)	(26)
Contributions by the plan participants	€ (4)	€ (5)

Actuarial gains (losses) arising from change in assumption recognized in profit loss.

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Disclosure of changes in financial position [line items]

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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)]

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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)]

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- Definition

The amount of expenses that the entity classifies as being administrative.

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The amount of benefits paid or payable for retirement benefit plans.

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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]]

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

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The amount of decrease in the fair value measurement of liabilities due to a change in one or more unobservable inputs to reflect reasonably possible alternative assumptions.

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The amount of employer contributions to retirement benefit plans.

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

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The amount of interest revenue calculated using the effective interest method. Effective interest method is the method that is used in the calculation of the amortised cost of a financial asset or a financial liability and in the allocation and recognition of the interest revenue or interest expense in profit or loss over the relevant period. [Refer: Revenue]

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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]]

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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]]

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The decrease (increase) in the net defined benefit liability (asset) resulting from the return on plan assets. The return on plans assets is interest, dividends and other revenue derived from the plan assets, together with realised and unrealised gains or losses on the plan assets, less any costs of managing plan assets and less any tax payable by the plan itself, other than tax included in the actuarial assumptions used to measure the present value of the defined benefit obligation. [Refer: Plan assets [member]; Net defined benefit liability (asset); Actuarial assumptions [member]]

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The increase (decrease) in net assets available for benefits resulting from transfers from (to) other retirement benefit plans. [Refer: Assets (liabilities) of benefit plan]

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