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Guarantees in Insurance Contracts - Summary of Liabilities for Guarantees That are Included in Valuation of Host Contracts, Net of Present Value of Expected Future Premiums (Detail) - EUR (€)
€ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Jan. 01, 2018
[1]
Liabilities under insurance contracts and reinsurance contracts issued [line items]      
Beginning balance [1] € 115,328    
Ending balance 123,454 € 115,328 [1]  
Net amount at risk 226,374 194,353 [1] € 194,063
The Netherlands [member]      
Liabilities under insurance contracts and reinsurance contracts issued [line items]      
Beginning balance 34,878    
Ending balance 40,554 34,878  
Net amount at risk 25,491 23,767  
The Netherlands [member] | Guaranteed Minimum Investment [member]      
Liabilities under insurance contracts and reinsurance contracts issued [line items]      
Beginning balance 5,063 4,719  
Incurred guarantee benefits 1,358 344  
Ending balance 6,422 5,063  
Account value 19,985 18,346  
Net amount at risk € 6,335 € 4,933  
[1] Amounts have been restated to reflect voluntary changes in accounting policies related to liability adequacy testing that was adopted by Aegon effective January 1, 2019. Refer to note 2.1.2 Voluntary changes in accounting policies for details about this change.