Employees - Summary of Movements in Liabilities (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of defined benefit plans [Line Items]
Current service cost	€ 245	€ 226	€ 271
Special termination benefits	4	6	9
Past service costs including losses/(gains) on curtailments	23	32	129
Settlements	4	(2)	6
Actuarial gain/(loss) arising from changes in demographic assumptions	222	(217)	(22)
Actuarial gain/(loss) arising from changes in financial assumptions	(210)	(2,963)	1,167
Actuarial gain/(loss) arising from experience adjustments	133	82	233
Liabilities [member]
Disclosure of defined benefit plans [Line Items]
Beginning balance	(24,356)	(23,062)
Current service cost	(245)	(226)
Employee contributions	0	0
Special termination benefits	(4)	(6)
Past service costs including losses/(gains) on curtailments	23	32
Settlements	12	(2)
Interest cost	(636)	(758)
Actuarial gain/(loss) arising from changes in demographic assumptions	222	(217)
Actuarial gain/(loss) arising from changes in financial assumptions	(210)	(2,963)
Actuarial gain/(loss) arising from experience adjustments	133	82
Benefit payments	1,239	1,326
Reclassification of benefits	8	2
Currency retranslation	871	1,436
Ending balance	(22,943)	(24,356)	(23,062)
Liabilities [member] \| United Kingdom [member]
Disclosure of defined benefit plans [Line Items]
Beginning balance	(10,981)	(10,602)
Current service cost	(114)	(89)
Employee contributions	0	0
Past service costs including losses/(gains) on curtailments	5	5
Interest cost	(286)	(347)
Actuarial gain/(loss) arising from changes in demographic assumptions	312	23
Actuarial gain/(loss) arising from changes in financial assumptions	(189)	(1,919)
Actuarial gain/(loss) arising from experience adjustments	144	29
Benefit payments	457	456
Currency retranslation	397	1,463
Ending balance	(10,255)	(10,981)	(10,602)
Liabilities [member] \| Netherlands [member]
Disclosure of defined benefit plans [Line Items]
Beginning balance	(4,877)	(4,443)
Current service cost	(6)	(3)
Employee contributions	0	0
Past service costs including losses/(gains) on curtailments	12	4
Interest cost	(86)	(109)
Actuarial gain/(loss) arising from changes in demographic assumptions	(96)	(19)
Actuarial gain/(loss) arising from changes in financial assumptions		(524)
Actuarial gain/(loss) arising from experience adjustments	(37)	46
Benefit payments	169	169
Reclassification of benefits	8	2
Ending balance	(4,913)	(4,877)	(4,443)
Liabilities [member] \| Rest of World [member]
Disclosure of defined benefit plans [Line Items]
Beginning balance	(8,498)	(8,017)
Current service cost	(125)	(134)
Employee contributions	0	0
Special termination benefits	(4)	(6)
Past service costs including losses/(gains) on curtailments	6	23
Settlements	12	(2)
Interest cost	(264)	(302)
Actuarial gain/(loss) arising from changes in demographic assumptions	6	(221)
Actuarial gain/(loss) arising from changes in financial assumptions	(21)	(520)
Actuarial gain/(loss) arising from experience adjustments	26	7
Benefit payments	613	701
Currency retranslation	474	(27)
Ending balance	€ (7,775)	€ (8,498)	€ (8,017)

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)]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2016-01-13
-Paragraph 141
-Subparagraph c
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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
-Name IAS
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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
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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 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 2016-01-13
-Paragraph 141
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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from past service cost and gains (losses) arising from settlements. [Refer: Gains (losses) arising from settlements, net defined benefit liability (asset); 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 decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan in respect of settlements. [Refer: Gains (losses) arising from settlements, net defined benefit liability (asset); Net defined benefit liability (asset); Defined benefit plans [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2016-01-13
-Paragraph 141
-Subparagraph g
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2016-03-30&anchor=para_141_g&doctype=Standard
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- Definition

The present value of the defined benefit obligation, less the fair value of the plan assets (if any). [Refer: Plan assets [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2016-01-13
-Paragraph 57
-Subparagraph a
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- Definition

The amount of expense in relation to termination benefits. Termination benefits are employee benefits provided in exchange for the termination of an employee's employment as a result of either: (a) an entity's decision to terminate an employee's employment before the normal retirement date; or (b) an employee's decision to accept an offer of benefits in exchange for the termination of employment. [Refer: Employee benefits expense]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2016-01-13
-Paragraph 171
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- Definition

Actuarial gains (losses) arising from experience adjustments, net defined benefit liability (asset).

+ References

No definition available.

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- Definition

Benefit Payments.

+ References

No definition available.

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- Definition

Interest cost on Pensions liabilities, which is the increase during a period in the present value of a defined benefit obligation which arises because the benefits are one period closer to settlement.

+ References

No definition available.

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- Definition

Reclassification of benefits.

+ References

No definition available.

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