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Financial Risks - Summary of Length of Time Security and Respective Realized Loss (Detail) - EUR (€)
€ in Millions
Dec. 31, 2019
Dec. 31, 2018
Disclosure of available for sale securities [line items]    
Debt securities € (66) € (378)
Not later than 1 year [member]    
Disclosure of available for sale securities [line items]    
Debt securities (32) (145)
> 12 months [member]    
Disclosure of available for sale securities [line items]    
Debt securities € (34) € (233)