Investment in associates and joint ventures - Summary of investments in associates and joint ventures (Details) - EUR (€) € in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2025	Dec. 31, 2024
Disclosure of investments in associates and joint ventures [line items]
Balance sheet value	€ 1,536	€ 1,679
Total assets	1,090,974	1,023,856
Total liabilities	€ 1,037,653	€ 970,158
TMB Public Company Limited \| TMBThanachart Bank Public Company Limited
Disclosure of investments in associates and joint ventures [line items]
Interest held	23.00%	23.00%
Fair value of listed invest-ments	€ 1,100	€ 1,164
Balance sheet value	1,191	1,266
Total assets	44,989	49,147
Total liabilities	38,627	42,554
Total income	434	1,474
Total expenses	306	1,050
Other investments in associates and joint ventures
Disclosure of investments in associates and joint ventures [line items]
Balance sheet value	€ 345	€ 412

The amount of a present economic resource controlled by the entity as a result of past events. Economic resource is a right that has the potential to produce economic benefits.

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The amount of investments in subsidiaries, joint ventures and associates in an entity's separate financial statements. [Refer: Total for all associates [member]; Total for all joint ventures [member]; Total for all subsidiaries [member]; Investments in subsidiaries reported in separate financial statements]

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The amount of a present obligation of the entity to transfer an economic resource as a result of past events. Economic resource is a right that has the potential to produce economic benefits.

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The proportion of ownership interest in an associate attributable to the entity. [Refer: Total for all associates [member]]

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The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims.

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