Employees - Summary of Movements in Assets (Details) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	€ 2,569	€ 2,993
Employee contributions	11	12
Settlements	2	1
Actual return on plan assets (excluding amounts in net finance income/charge)	131	(6,483)
Change in asset ceiling excluding amounts included in interest expenses	(6)	(184)
Employer contributions	407	303
Benefit payments	0	0
Other	0	13
Currency retranslation	186	(63)
Net defined benefit liability (asset)	2,401	2,569
Increase (decrease) resulting from reclassification to defined benefit	0
Fair value of assets before irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	19,367	26,693
Net defined benefit liability (asset)	20,178	19,367
Irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	(234)	(50)
Interest income	(7)	2
Currency retranslation	(8)	(2)
Net defined benefit liability (asset)	(255)	(234)
Fair value of assets after irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	19,133	26,643
Net defined benefit liability (asset)	19,923	19,133
Fair value of assets
Disclosure of defined benefit plans [line items]
Employee contributions	11	12
Settlements	(1)	0
Actual return on plan assets (excluding amounts in net finance income/charge)	131	(6,483)
Change in asset ceiling excluding amounts included in interest expenses	(6)	(184)
Interest income	859	496
Employer contributions	407	303
Benefit payments	(1,122)	(1,184)
Other	371	(2)
Currency retranslation	140	(468)
Increase (decrease) resulting from reclassification to defined benefit	(368)
UK
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	1,866	2,879
Employee contributions	0	1
Settlements	0	0
Actual return on plan assets (excluding amounts in net finance income/charge)	(227)	(4,870)
Change in asset ceiling excluding amounts included in interest expenses	0	0
Employer contributions	50	66
Benefit payments	0	0
Other	0	0
Currency retranslation	44	(99)
Net defined benefit liability (asset)	1,429	1,866
UK \| Fair value of assets before irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	8,704	14,332
Net defined benefit liability (asset)	8,679	8,704
UK \| Irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	0	0
Interest income	0	0
Currency retranslation	0	0
Net defined benefit liability (asset)	0	0
UK \| Fair value of assets after irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	8,704	14,332
Net defined benefit liability (asset)	8,679	8,704
UK \| Fair value of assets
Disclosure of defined benefit plans [line items]
Employee contributions	0	1
Settlements	0	0
Actual return on plan assets (excluding amounts in net finance income/charge)	(227)	(4,870)
Change in asset ceiling excluding amounts included in interest expenses	0	0
Interest income	432	264
Employer contributions	50	66
Benefit payments	(459)	(511)
Other	0	0
Currency retranslation	179	(578)
The Netherlands
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	1,609	1,162
Employee contributions	0	0
Settlements	0	0
Actual return on plan assets (excluding amounts in net finance income/charge)	146	(668)
Change in asset ceiling excluding amounts included in interest expenses	0	0
Employer contributions	9	8
Benefit payments	0	0
Other	0	(1)
Currency retranslation	0	0
Net defined benefit liability (asset)	1,483	1,609
The Netherlands \| Fair value of assets before irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	5,343	6,099
Net defined benefit liability (asset)	5,514	5,343
The Netherlands \| Irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	0	0
Interest income	0	0
Currency retranslation	0	0
Net defined benefit liability (asset)	0	0
The Netherlands \| Fair value of assets after irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	5,343	6,099
Net defined benefit liability (asset)	5,514	5,343
The Netherlands \| Fair value of assets
Disclosure of defined benefit plans [line items]
Employee contributions	0	0
Settlements	0	0
Actual return on plan assets (excluding amounts in net finance income/charge)	146	(668)
Change in asset ceiling excluding amounts included in interest expenses	0	0
Interest income	194	66
Employer contributions	9	8
Benefit payments	(178)	(161)
Other	0	(1)
Currency retranslation	0	0
Rest of world
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	(906)	(1,048)
Employee contributions	11	11
Settlements	2	1
Actual return on plan assets (excluding amounts in net finance income/charge)	212	(945)
Change in asset ceiling excluding amounts included in interest expenses	(6)	(184)
Employer contributions	348	229
Benefit payments	0	0
Other	0	14
Currency retranslation	142	36
Net defined benefit liability (asset)	(511)	(906)
Rest of world \| Fair value of assets before irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	5,320	6,262
Net defined benefit liability (asset)	5,985	5,320
Rest of world \| Irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	(234)	(50)
Interest income	(7)	2
Currency retranslation	(8)	(2)
Net defined benefit liability (asset)	(255)	(234)
Rest of world \| Fair value of assets after irrecoverable surplus
Disclosure of defined benefit plans [line items]
Net defined benefit liability (asset)	5,086	6,212
Net defined benefit liability (asset)	5,730	5,086
Rest of world \| Fair value of assets
Disclosure of defined benefit plans [line items]
Employee contributions	11	11
Settlements	(1)	0
Actual return on plan assets (excluding amounts in net finance income/charge)	212	(945)
Change in asset ceiling excluding amounts included in interest expenses	(6)	(184)
Interest income	233	166
Employer contributions	348	229
Benefit payments	(485)	(512)
Other	371	(1)
Currency retranslation	€ (39)	€ 110

The decrease (increase) in net defined benefit liability (asset) resulting from contributions to a defined benefit plan by the employer. [Refer: Net defined benefit liability (asset); Defined benefit plans [member]]

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-Name IAS
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-IssueDate 2023-01-01
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-URIDate 2023-03-23

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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

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from the gain (loss) on changes in the effect of limiting a net defined benefit asset to the asset ceiling, excluding amounts included in interest income or expense. [Refer: Interest income (expense); Net defined benefit liability (asset); Increase (decrease) in net defined benefit liability (asset) resulting from interest expense (income)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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-IssueDate 2023-01-01
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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
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-IssueDate 2023-01-01
-Paragraph 141
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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
-Name IAS
-Number 19
-IssueDate 2023-01-01
-Paragraph 141
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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)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2023-01-01
-Paragraph 141
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- Definition

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]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2023-01-01
-Paragraph 140
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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 2023-01-01
-Paragraph 141
-Subparagraph g
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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: Decrease (increase) in net defined benefit liability (asset) resulting from gains (losses) arising from settlements; Net defined benefit liability (asset); Defined benefit plans [member]]

+ References

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- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from the return on plan assets, excluding amounts included in interest income or expense. The return on plan 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]; Increase (decrease) in net defined benefit liability (asset) resulting from interest expense (income)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2023-01-01
-Paragraph 141
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-URIDate 2023-03-23

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- Definition

Decrease (Increase) In Net Defined Benefit Liability (Asset) Resulting From Reclassification

+ References

No definition available.

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