Defined Benefit Plans - Summary of Estimated Approximate Effects on Defined Benefit Obligation (Detail) - EUR (€) € in Millions	Dec. 31, 2025	Dec. 31, 2024
Transamerica [member] \| Demographic actuarial assumption on mortality rates by 10% Variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	€ (40)	€ (46)
Decrease in actuarial assumptions	44	51
Transamerica [member] \| Financial actuarial assumptions of discount rates by 100 basis points variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	(163)	(183)
Decrease in actuarial assumptions	201	232
Transamerica [member] \| Finance actuarial assumption on salary increase rate by 100 basis points variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	4	4
Decrease in actuarial assumptions	(3)	(4)
Transamerica [member] \| Financial actuarial assumptions of health care trend rates by 100 bps variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	9	12
Decrease in actuarial assumptions	(9)	(10)
Aegon United Kingdom [member] \| Demographic actuarial assumption on mortality rates by 10% Variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	(20)	(21)
Decrease in actuarial assumptions	21	23
Aegon United Kingdom [member] \| Financial actuarial assumptions of discount rates by 100 basis points variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	(103)	(114)
Decrease in actuarial assumptions	126	142
Aegon United Kingdom [member] \| Financial actuarial assumptions of price inflation trend rates by 100 bps variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	110	50
Decrease in actuarial assumptions	(101)	(95)
Aegon Employees Netherlands BV [Member] \| Demographic actuarial assumption on mortality rates by 10% Variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	(1)	(1)
Decrease in actuarial assumptions	1	1
Aegon Employees Netherlands BV [Member] \| Financial actuarial assumptions of discount rates by 100 basis points variation [member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Increase in actuarial assumptions	(12)	(13)
Decrease in actuarial assumptions	€ 16	€ 17

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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by a decrease in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [domain]]

+ References

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The increase (decrease) in a defined benefit obligation that would have been caused by an increase in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [domain]]

+ References

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