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Guarantees in Insurance Contracts - Additional Information (Detail) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2013
Dec. 31, 1999
Dec. 31, 2017
Disclosure of insurance contracts contractual obligations [Line Items]          
Period of which return of premium guarantee payable   14 years      
Re insured account value € 2,434 € 2,663     € 3,431
Guaranteed remaining balance € 1,100 1,100      
Derivative insurance contract description Aegon entered into a derivative program to mitigate the overall exposure to equity market and interest rate risks associated with the reinsurance contract. This program involves selling equity futures contracts and equity total return swap contracts (S&P 500, Midcap, Russell 2000, and the MCSI EAFE index in accordance with Aegon's exposure) to mitigate the effect of equity market movement on the reinsurance contract and the purchase of interest rate swaps, treasury futures and treasury forwards to mitigate the effect of movements in interest rates on the reinsurance contracts.        
Fixed annuity product balance € 234 243      
Increase (decrease) in guarantee reserves 1,937 (1,081)      
Guarantee reserve 9,645 7,708      
GMWB [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Derivative contract value 37 36      
Reinsurance assets [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Re insured account value € 1,800 € 1,700      
First five years [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Long-term forward interest rate assumption 25.00%        
Maturity year 2020 [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Volatility assumption of S&P 500 index   23.30%      
The Netherlands [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Older generation guarantee, percentage 4.00%        
Percentage of guarantee decreased     0.00% 3.00%  
The Netherlands [member] | Minimum investment return guaranteed [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Guarantees profit sharing maximum, percentage 0.00%        
Contract period 5 years        
Guarantees fair value contributes net loss before tax earnings € 424 € 56      
Guarantee reserve contributed before tax 1,840 527      
Gain (Loss) related to increasing own credit spreads (42) 148      
Gain related to increase in equity market (1,585) (532)      
Gain related to decreases in equity volatilities (12) (8)      
Increase in risk free rates 3,281 32      
Other contributed gain (loss) € 273 € (233)      
The Netherlands [member] | Bottom of range [member] | Minimum investment return guaranteed [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Adjusted technical interest rates 3.00%        
Effective interest rate percentage 0.00%        
The Netherlands [member] | Top of range [member] | Minimum investment return guaranteed [member]          
Disclosure of insurance contracts contractual obligations [Line Items]          
Adjusted technical interest rates 4.00%