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Critical Accounting Estimates and Judgment in Applying Accounting Policies - Additional Information (Detail) - EUR (€)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of changes in accounting estimates [line items]      
Increase decrease in earning before tax due to actuarial assumption and model updates € 196,000,000 € 121,000,000  
Uniform grading period 10-year    
Description of voluntary changes For the years 2017 through 2019, Aegon kept its long-term equity market return assumption for the estimated gross profits on variable life and variable annuity products in the Americas at 8%. During the three year period, the long-term assumption for 10-year US Treasury yields was 4.25% and the uniform grading period was 10 years. Aegon’s assumed returns for US separate account bond funds are 4% over the next 10 years and 6% thereafter. The long term credit spread assumption, net of assumed defaults and expenses, on our most common corporate bonds is 114bps. The 90-day Treasury yield was 1.55%, 2.37% and 1.39% at December 31, 2019, 2018 and 2017, respectively. During the period 2017 to 2019 the 90-day Treasury yield was assumed to have a uniform grading over 10 years to 2.5%. On a quarterly basis, the estimated gross profits are updated for the difference between the estimated market return and the actual market return.    
Percentage of increase in mortality assumption 10.00%    
Decrease in net income due to increase of mortality assumption € 204,000,000 207,000,000  
Percentage of increase in the lapse rate assumption 20.00%    
Increase in net income due to increase in lapse rate assumptions € 126,000,000 89,000,000  
Interest rate, measurement input [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage increase in inputs of liability adequacy test 1.00%    
Percentage decrease in inputs of liability adequacy test 1.00%    
Aegon N.V [member]      
Disclosure of changes in accounting estimates [line items]      
Decrease in net income due to possible changes in other assumptions € 13,000,000 € 9,000,000  
10-year US treasury yields [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage of rate of return 4.25%    
Bonds [member]      
Disclosure of changes in accounting estimates [line items]      
Long term credit spread assumption   1.14%  
Bonds [member] | Grading over 10 years [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage of rate of return 4.00%    
Bonds [member] | Grading after 10 years [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage of rate of return 6.00%    
90-day treasury yield [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage of rate of return 1.55% 2.37% 1.39%
90-day treasury yield [member] | Grading over 10 years [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage of rate of return 2.50% 2.50% 2.50%
Americas [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage of long-term equity market return assumption 8.00%    
United States [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage of decrease in expected long-term equity growth rate   1.00%  
Decrease in DPAC and VOBA balances and reserve € 111,000,000 € 148,000,000  
DPAC and VOBA balance 2,700,000,000 2,600,000,000  
United States [member] | Long term care products [member]      
Disclosure of changes in accounting estimates [line items]      
Gross present value reserve margin € 251,000,000 35,000,000  
Increase in incidence rates resulting in increase of gross present value, percentage 5.00%    
Increase in gross present value reserve after increase in incidence rate € 178,000,000 170,000,000  
Decrease in incidence rates resulting in decrease of gross present value, percentage 5.00%    
Decrease in gross present value decrease after decrease in incidence rate € 178,000,000 170,000,000  
Increase in gross present value reserve after removing the morbidity improvement 535,000,000 500,000,000  
Increase in gross present value reserve related to loss recognition block after removing the morbidity improvement € 445,000,000 425,000,000  
Percentage of decrease in mortality resulting in gross present value reserve increase 10.00%    
Increase in gross present value reserve after decrease in mortality € 89,000,000 85,000,000  
Decrease in gross present value reserve after increase in mortality € 89,000,000 85,000,000  
Percentage of increase in mortality resulting in gross present value reserve decrease 10.00%    
Decrease in gross present value reserve after removing mortality improvement € 89,000,000 € 85,000,000  
The Netherlands [member]      
Disclosure of changes in accounting estimates [line items]      
Liability Adequency Test Deficit 5,100,000,000    
Loss Recognition 3,400,000,000    
Net Deficits € 1,700,000,000    
Liquidity Premium Rate 0.05%    
The Netherlands [member] | Interest rate, measurement input [member]      
Disclosure of changes in accounting estimates [line items]      
Increase of deficit in liability adequacy test € 4,700,000,000    
Decrease of deficit in liability adequacy test € 3,500,000,000    
The Netherlands [member] | Credit spread, measurement input [member]      
Disclosure of changes in accounting estimates [line items]      
Percentage increase in inputs of liability adequacy test 0.50%    
Increase of deficit in liability adequacy test € 200,000,000    
Decrease of deficit in liability adequacy test € 200,000,000    
Percentage decrease in inputs of liability adequacy test 0.50%    
The Netherlands [member] | Mortgage Measurement Input [Member]      
Disclosure of changes in accounting estimates [line items]      
Percentage increase in inputs of liability adequacy test 0.50%    
Increase of deficit in liability adequacy test € 600,000,000    
Decrease of deficit in liability adequacy test € 600,000,000    
Percentage decrease in inputs of liability adequacy test 0.50%