Employees - Summary of Movements in Liabilities (Detail) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of defined benefit plans [line items]
Current service cost	€ (223)	€ (216)	€ (220)
Special termination benefits	(37)	(5)	(16)
Past service costs including (losses)/gains on curtailments	(20)	(65)	41
Actuarial gain/(loss) arising from changes in demographic assumptions	(246)	(183)	(42)
Actuarial gain/(loss) arising from changes in financial assumptions	1,414	2,138	(611)
Actuarial gain/(loss) arising from experience adjustments	78	12	(18)
Liabilities [Member]
Disclosure of defined benefit plans [line items]
Beginning balance	(23,922)	(21,754)
Current service cost	(223)	(216)
Special termination benefits	(37)	(5)
Past service costs including (losses)/gains on curtailments	20	65
Settlements	74	(2)
Interest cost	(445)	(603)
Actuarial gain/(loss) arising from changes in demographic assumptions	246	183
Actuarial gain/(loss) arising from changes in financial assumptions	(1,414)	(2,138)
Actuarial gain/(loss) arising from experience adjustments	(78)	(12)
Benefit payments	1,140	1,208
Others	(38)	(20)
Currency retranslation	958	(628)
Ending balance	(23,719)	(23,922)	(21,754)
Liabilities [Member] \| United Kingdom [Member]
Disclosure of defined benefit plans [line items]
Beginning balance	(11,001)	(9,739)
Current service cost	(114)	(104)
Past service costs including (losses)/gains on curtailments	17	56
Interest cost	(208)	(276)
Actuarial gain/(loss) arising from changes in demographic assumptions	(1)	157
Actuarial gain/(loss) arising from changes in financial assumptions	(806)	(955)
Actuarial gain/(loss) arising from experience adjustments	(67)	(44)
Benefit payments	467	455
Others	(44)
Currency retranslation	609	(551)
Ending balance	(11,148)	(11,001)	(9,739)
Liabilities [Member] \| Netherlands [Member]
Disclosure of defined benefit plans [line items]
Beginning balance	(5,097)	(4,664)
Current service cost	(3)	(4)
Interest cost	(55)	(82)
Actuarial gain/(loss) arising from changes in demographic assumptions	245	14
Actuarial gain/(loss) arising from changes in financial assumptions	(354)	(511)
Actuarial gain/(loss) arising from experience adjustments	(6)	(15)
Benefit payments	166	165
Others	44
Ending balance	(5,060)	(5,097)	(4,664)
Liabilities [Member] \| All other countries [member]
Disclosure of defined benefit plans [line items]
Beginning balance	(7,824)	(7,351)
Current service cost	(106)	(108)
Special termination benefits	(37)	(5)
Past service costs including (losses)/gains on curtailments	3	9
Settlements	74	(2)
Interest cost	(182)	(245)
Actuarial gain/(loss) arising from changes in demographic assumptions	2	12
Actuarial gain/(loss) arising from changes in financial assumptions	(254)	(672)
Actuarial gain/(loss) arising from experience adjustments	(5)	47
Benefit payments	507	588
Others	(38)	(20)
Currency retranslation	349	(77)
Ending balance	€ (7,511)	€ (7,824)	€ (7,351)

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 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 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

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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.

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No definition available.

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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)]

+ References

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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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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

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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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- 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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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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Payments in respect of settlements net defined benefit obligation.

+ References

No definition available.

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