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Transfers of Financial Assets - Additional Information (Detail) - EUR (€)
Dec. 31, 2019
Dec. 31, 2018
Disclosure of financial assets [line items]    
Transferred financial assets with continuing involvement that are derecognized in their entirely € 0 € 0
Amount of collateral pledged for derivative transactions 2,400,000,000 1,400,000,000
The Netherlands [member]    
Disclosure of financial assets [line items]    
Mortgage loan pledged as security for notes issued € 5,500,000,000 € 6,000,000,000