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Financial Risks - Summary of Composition of Shares by Industry Sector in Unrealized Loss Position (Detail) - Aegon US, NL [member] - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Disclosure of impairment losses on shares [line items]    
Carrying value of instruments with unrealized losses € 58 € 86
Unrealized losses (24) (20)
Financial Industry [member]    
Disclosure of impairment losses on shares [line items]    
Carrying value of instruments with unrealized losses 28 49
Unrealized losses (10) (15)
Other industry [member]    
Disclosure of impairment losses on shares [line items]    
Carrying value of instruments with unrealized losses 30 37
Unrealized losses € (14) € (6)