Fair value of assets and liabilities - Additional information (Details) - EUR (€) € in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Disclosure of fair value measurement of assets and liabilities [line items]
Financial assets classified as level 3 based on quoted price	€ 7,200	€ 7,000
Percentage on financial asset based on unadjusted quoted price	79.10%	76.70%
Amount of risk neutral designed financial assets	€ 300	€ 300
Remaining financial assets classified as level 3 using valuation techniques	1,600	1,800
Financial liabilities measured at fair value	102,649	94,638
Financial liabilities classified as level 3 based on unadjusted quoted price	230	360
Financial liabilities designed to be fully neutral in terms of market risk	300	300
Debt securities
Disclosure of fair value measurement of assets and liabilities [line items]
Transfer from level 2 to level 1	400
Level 3
Disclosure of fair value measurement of assets and liabilities [line items]
Fair value of swap	9,081	€ 9,118	€ 7,526
Percentage on financial asset based on unadjusted quoted price		50.00%
Financial liabilities measured at fair value	€ 564	€ 729
Percentage on financial liabilities based on unadjusted quoted prices in inactive markets	41.00%
Remaining financial liabilities classified as level 3 using valuation techniques	€ 100	€ 100

The fair value of financial assets. [Refer: At fair value [member]; Financial assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2023-01-01
-Paragraph 25
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2023-en-r&anchor=para_25&doctype=Standard
-URIDate 2023-03-23

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- Definition

The amount of financial liabilities that meet either of the following conditions: (a) they meet the definition of held for trading; or (b) upon initial recognition they are designated by the entity as at fair value through profit or loss. An entity may use this designation only when permitted by paragraph 4.3.5 of IFRS 9 (embedded derivatives) or when doing so results in more relevant information, because either: (a) it eliminates or significantly reduces a measurement or recognition inconsistency (sometimes referred to as ‘an accounting mismatch’) that would otherwise arise from measuring assets or liabilities or recognising the gains and losses on them on different bases; or (b) a group of financial liabilities or financial assets and financial liabilities is managed and its performance is evaluated on a fair value basis, in accordance with a documented risk management or investment strategy, and information about the group is provided internally on that basis to the entity’s key management personnel (as defined in IAS 24). [Refer: At fair value [member]; Key management personnel of entity or parent [member]; Derivatives [member]; Financial assets; Financial liabilities]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2023-01-01
-Paragraph 8
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2023-en-r&anchor=para_8_e&doctype=Standard
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- Definition

The amount of transfers out of Level 2 and into Level 1 of the fair value hierarchy of assets held at the end of the reporting period. [Refer: Level 1 of fair value hierarchy [member]; Level 2 of fair value hierarchy [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 13
-IssueDate 2023-01-01
-Paragraph 93
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2023-en-r&anchor=para_93_c&doctype=Standard
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- Definition

Amount of financial liabilities designed to be fully neutral.

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Amount of financial assets designed to be fully neutral.

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Disclosure of fair value measurement of assets and liabilities.

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Financial assets classified as Level 3 based on quoted price.

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Financial Liabilities classified as Level 3 based on unadjusted quoted price.

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Percentage on financial assets based on unadjusted quoted prices in inactive markets.

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Percentage On Financial Liabilities Based On Unadjusted Quoted Prices In Inactive Markets

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Remaining financial assets classified as level 3.

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Remaining financial liabilities classified as level 3 that incorporates certain inputs that are unobservable.

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