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Pensions and Other Post-employment Benefit Obligations - Summary of Amounts Recognized in Unaudited Interim Consolidated Income Statement (Detail) - Consolidated Income Statement [member] - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disclosure of changes in financial position [line items]
Current service cost	€ (5)	€ (7)	€ (11)	€ (13)
Past service cost	0	0	0	22
Net interest	(4)	(4)	(8)	(9)
Immediate recognition of gains / (losses) arising over the period	0	0	0	0
Administrative expenses	(1)	0	(1)	(1)
Total	(10)	(11)	(20)	(1)
Pension benefits [member]
Disclosure of changes in financial position [line items]
Current service cost	(3)	(4)	(8)	(9)
Past service cost	0	0	0	18
Net interest	(2)	(2)	(4)	(4)
Immediate recognition of gains / (losses) arising over the period	0	0	0	0
Administrative expenses	(1)	0	(1)	(1)
Total	(6)	(6)	(13)	4
Other benefits [member]
Disclosure of changes in financial position [line items]
Current service cost	(2)	(3)	(3)	(4)
Past service cost	0	0	0	4
Net interest	(2)	(2)	(4)	(5)
Immediate recognition of gains / (losses) arising over the period	0	0	0	0
Total	€ (4)	€ (5)	€ (7)	€ (5)

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- Definition

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

+ References

No definition available.

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- Definition

Defined benefit plan net periodic benefit cost.

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Disclosure of changes in financial position [line items]

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- Definition

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

+ References

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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

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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from the passage of time. [Refer: Interest expense; Net defined benefit liability (asset)]

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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]]

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