Transfer of Financial Assets, Assets Pledged and Received as Collateral - Fair Value of collateral received (Detail) - EUR (€) € in Millions	Dec. 31, 2025	Dec. 31, 2024
Transfers of Financial Assets [Abstract]
Securities and other financial assets accepted as collateral	€ 557,837	€ 479,022
Of which:
Collateral sold or repledged	€ 431,792	€ 366,245

The fair value of collateral sold or repledged that was permitted to be sold or repledged in the absence of default by the owner of the collateral. [Refer: At fair value [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph 15
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_15_b&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_AssetsSoldOrRepledgedAsCollateralAtFairValue
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant