Employees - Summary of Amounts Recognised in Statement of Comprehensive Income on Remeasurement of Net Defined Benefit Liability (Details) - EUR (€) € in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Classes of employee benefits expense [abstract]
Return on plan assets excluding amounts included in net finance income/(cost)	€ 131	€ (6,483)	€ 1,958
Change in asset ceiling excluding amounts included in finance cost	(6)	(184)	(17)
Actuarial gains/(losses) arising from changes in demographic assumptions	98	(24)	(4)
Actuarial gains/(losses) arising from changes in financial assumptions	(552)	6,914	342
Experience gains/(losses) arising on pension plan and other benefit plan liabilities	(416)	(760)	126
Total of defined benefit costs recognised in other comprehensive income	€ (745)	€ (537)	€ 2,405

The amount of other comprehensive income, before tax, 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: Other comprehensive income, before tax, gains (losses) on remeasurements of defined benefit plans] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions]

Name:	ifrs-full_ActuarialGainsLossesArisingFromChangesInDemographicAssumptionsBeforeTaxDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of other comprehensive income, before tax, 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: Other comprehensive income, before tax, gains (losses) on remeasurements of defined benefit plans] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions]

+ References

+ Details

Name:	ifrs-full_ActuarialGainsLossesArisingFromChangesInFinancialAssumptionsBeforeTaxDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of other comprehensive income, before tax, 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: Other comprehensive income, before tax, gains (losses) on remeasurements of defined benefit plans] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from actuarial gains (losses) arising from experience adjustments]

+ References

+ Details

Name:	ifrs-full_ActuarialGainsLossesArisingFromExperienceAdjustmentsBeforeTaxDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	ifrs-full_ClassesOfEmployeeBenefitsExpenseAbstract
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of other comprehensive income, before tax, 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: Other comprehensive income, before tax, gains (losses) on remeasurements of defined benefit plans] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from gain (loss) on changes in effect of limiting net defined benefit asset to asset ceiling excluding interest income or expense]

+ References

+ Details

Name:	ifrs-full_GainsLossesOnChangesInEffectOfLimitingNetDefinedBenefitAssetToAssetCeilingExcludingInterestIncomeOrExpenseBeforeTaxDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of other comprehensive income, before tax, related to gains (losses) on remeasurements of defined benefit plans, which comprise actuarial gains and losses; the return on plan assets, excluding amounts included in net interest on the net defined benefit liability (asset); and any change in the effect of the asset ceiling, excluding amounts included in net interest on the net defined benefit liability (asset). [Refer: Other comprehensive income; Defined benefit plans [member]; Plan assets [member]; Net defined benefit liability (asset)] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from gain (loss) on remeasurement in other comprehensive income]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2023-01-01
-Paragraph 135
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2023-en-r&anchor=para_135_b&doctype=Standard
-URIDate 2023-03-23

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2023-01-01
-Paragraph 91
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2023-en-r&anchor=para_91_b&doctype=Standard
-URIDate 2023-03-23

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2023-01-01
-Paragraph 7
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2023-en-r&anchor=para_7&doctype=Standard
-URIDate 2023-03-23

+ Details

Name:	ifrs-full_OtherComprehensiveIncomeBeforeTaxGainsLossesOnRemeasurementsOfDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of other comprehensive income, before tax, resulting from the return on plan assets, excluding amounts included in interest expense (income) arising from defined benefit plans. 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: Other comprehensive income; Defined benefit plans [member]; Plan assets [member]; Other comprehensive income, before tax, gains (losses) on remeasurements of defined benefit plans] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from return on plan assets excluding interest income or expense]

+ References

+ Details

Name:	ifrs-full_ReturnOnPlanAssetsExcludingInterestIncomeOrExpenseBeforeTaxDefinedBenefitPlans
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration