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Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2019
EUR (€)
€ / shares
Dec. 31, 2018
EUR (€)
Dec. 31, 2017
EUR (€)
Jan. 01, 2019
EUR (€)
May 15, 2018
USD ($)
Disclosure of summary of significant accounting policies [line items]          
Right-of-use assets € 255,000,000        
Lease liabilities € 311,000,000     € 285,000,000  
Description of hedging relationship considered highly effective A hedging relationship is considered highly effective if the results of the hedging instrument are within a ratio of 80% to 125% of the results of the hedged item.        
Impairment of available-for-sale equity instruments, significant or prolonged decline, description Significant or prolonged decline is defined as an unrealized loss position for generally more than six months or a fair value of less than 80% of the cost price of the investment.        
Threshold period for investment in equity securities in a continuous decline in value to be considered More than six months        
Threshold percentage by which investments in equity securities have declined in value to be considered 80.00%        
Gain or loss is recognized in on purchase, sale, issue or cancellation of instruments € 0        
Net income after accounting policy changes € 1,239,000,000 € 711,000,000 [1] € 2,469,000,000 [1]    
Impact on earnings per share basic and diluted | € / shares € 0.01        
Aegon N.V [member]          
Disclosure of summary of significant accounting policies [line items]          
Net income after accounting policy changes € (141,000,000) € (122,000,000) € (42,000,000)    
Aegon N.V [member] | Accounting Policy Change Liquidity Adequacy Testing [Member]          
Disclosure of summary of significant accounting policies [line items]          
Net income after accounting policy changes 19,000,000        
Changes in equity 19,000,000        
Increase decrease through other changes liabilities under insurance and reinsurance contracrs 25,000,000        
Increase decrease in other liabilities 6,000,000        
Equipment [member]          
Disclosure of summary of significant accounting policies [line items]          
Right-of-use assets 23,000,000        
Non-cumulative subordinated notes [member]          
Disclosure of summary of significant accounting policies [line items]          
Principal amount | $         $ 525,000,000
IFRS 16 [member]          
Disclosure of summary of significant accounting policies [line items]          
Right-of-use assets 235,000,000        
Lease liabilities 285,000,000        
Impact on shareholders' equity expected 41,000,000        
Weigted average incremental borrowing rate for lease liabilities       3.46%  
Increase (decrease) through appropriation of retained earnings, equity (3,000,000)        
IFRS 16 [member] | Properties [member]          
Disclosure of summary of significant accounting policies [line items]          
Right-of-use assets 212,000,000        
IFRS 16 [member] | Buildings [member] | United Kingdom [member]          
Disclosure of summary of significant accounting policies [line items]          
Right-of-use assets 116,000,000        
IFRS 16 [member] | Buildings [member] | US [member]          
Disclosure of summary of significant accounting policies [line items]          
Right-of-use assets € 50,000,000        
[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.