Fair Value - Summary of Carrying Amounts of Financial Assets and Financial Liabilities that are Classified as at Fair Value Through Profit or Loss (Detail) - EUR (€) € in Millions	Dec. 31, 2025	Dec. 31, 2024
Financial assets at fair value through profit or loss [member]
Disclosure of fair value financial assets and liabilities [line items]
Trading	€ 7,695	€ 8,267
Designated	218,317	220,637
Financial liabilities at fair value through profit or loss, category [member]
Disclosure of fair value financial assets and liabilities [line items]
Trading	597	1,331
Designated	85,161	79,078
Investments - Aegon risk [member] \| Financial assets at fair value through profit or loss [member]
Disclosure of fair value financial assets and liabilities [line items]
Trading	7,306	7,661
Designated	2,066	2,356
Investments - Policyholder risk [member] \| Financial assets at fair value through profit or loss [member]
Disclosure of fair value financial assets and liabilities [line items]
Trading	0	0
Designated	216,251	218,281
Investment contracts without DPF - Policyholder risk [member] \| Financial liabilities at fair value through profit or loss, category [member]
Disclosure of fair value financial assets and liabilities [line items]
Trading	0	0
Designated	85,161	79,078
Derivatives not designated as hedges [member] \| Financial assets at fair value through profit or loss [member]
Disclosure of fair value financial assets and liabilities [line items]
Trading	390	606
Designated	0	0
Derivatives not designated as hedges [member] \| Financial liabilities at fair value through profit or loss, category [member]
Disclosure of fair value financial assets and liabilities [line items]
Trading	597	1,331
Designated	€ 0	€ 0