Employees - Summary of Movements in Liabilities (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of defined benefit plans [line items]
Current service cost	€ (220)	€ (245)	€ (226)
Special termination benefits	(16)	(4)	(6)
Past service costs including (losses)/gains on curtailments	41	(23)	(32)
Settlements		(4)	2
Actuarial gain/(loss) arising from changes in demographic assumptions	(42)	(222)	217
Actuarial gain/(loss) arising from changes in financial assumptions	(611)	210	2,963
Actuarial gain/(loss) arising from experience adjustments	(18)	(133)	(82)
Liabilities [Member]
Disclosure of defined benefit plans [line items]
Beginning balance	(22,943)	(24,356)
Current service cost	(220)	(245)
Employee contributions	0	0
Special termination benefits	(16)	(4)
Past service costs including (losses)/gains on curtailments	(41)	23
Settlements	1	12
Interest cost	(576)	(636)
Actuarial gain/(loss) arising from changes in demographic assumptions	42	222
Actuarial gain/(loss) arising from changes in financial assumptions	611	(210)
Actuarial gain/(loss) arising from experience adjustments	18	133
Benefit payments	1,199	1,239
Currency retranslation	161	871
Others	10	8
Ending balance	(21,754)	(22,943)	(24,356)
Liabilities [Member] \| United Kingdom [Member]
Disclosure of defined benefit plans [line items]
Beginning balance	(10,255)	(10,981)
Current service cost	(109)	(114)
Employee contributions	0	0
Past service costs including (losses)/gains on curtailments	(46)	5
Interest cost	(254)	(286)
Actuarial gain/(loss) arising from changes in demographic assumptions		312
Actuarial gain/(loss) arising from changes in financial assumptions	351	(189)
Actuarial gain/(loss) arising from experience adjustments	(45)	144
Benefit payments	472	457
Currency retranslation	147	397
Ending balance	(9,739)	(10,255)	(10,981)
Liabilities [Member] \| Netherlands [Member]
Disclosure of defined benefit plans [line items]
Beginning balance	(4,913)	(4,877)
Current service cost	(4)	(6)
Employee contributions	0	0
Past service costs including (losses)/gains on curtailments	8	12
Interest cost	(87)	(86)
Actuarial gain/(loss) arising from changes in demographic assumptions	53	(96)
Actuarial gain/(loss) arising from changes in financial assumptions	84
Actuarial gain/(loss) arising from experience adjustments	37	(37)
Benefit payments	166	169
Others	(8)	8
Ending balance	(4,664)	(4,913)	(4,877)
Liabilities [Member] \| All other countries [member]
Disclosure of defined benefit plans [line items]
Beginning balance	(7,775)	(8,498)
Current service cost	(107)	(125)
Employee contributions	0	0
Special termination benefits	(16)	(4)
Past service costs including (losses)/gains on curtailments	(3)	6
Settlements	1	12
Interest cost	(235)	(264)
Actuarial gain/(loss) arising from changes in demographic assumptions	(11)	6
Actuarial gain/(loss) arising from changes in financial assumptions	176	(21)
Actuarial gain/(loss) arising from experience adjustments	26	26
Benefit payments	561	613
Currency retranslation	14	474
Others	18
Ending balance	€ (7,351)	€ (7,775)	€ (8,498)

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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- 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

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The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from experience adjustments that result in remeasurements of the net defined benefit liability (asset). Experience adjustments deal with the effects of differences between the previous actuarial assumptions and what has actually occurred. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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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
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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
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- Definition

The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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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
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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from changes that the entity does not separately disclose in the same statement or note. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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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
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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 141
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- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan 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

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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

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-IssueDate 2017-01-01
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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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