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Commitments and Contingencies - Summary of Commitments through Purchase and Sale Transactions of Investments (Detail) - EUR (€)
€ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Real estate [member]    
Disclosure of purchase and sale transactions of investments [line items]    
Purchase € 168 € 156
Sale 3 66
Mortgage loans [member]    
Disclosure of purchase and sale transactions of investments [line items]    
Purchase 859 3,187
Sale 79 67
Private loans [member]    
Disclosure of purchase and sale transactions of investments [line items]    
Purchase 394 1,224
Other [member]    
Disclosure of purchase and sale transactions of investments [line items]    
Purchase € 1,824 € 2,222