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v3.20.1

Defined Benefit Plans - Target Allocation of Plan Assets for Retirement Benefit Plans for the Next Annual Period (Detail) | Dec. 31, 2019 | Dec. 31, 2018
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Disclosure of sensitivity analysis for actuarial assumptions [Line Items] |  |
Equity instruments | 4.00% | 3.00%
Debt instruments | 19.00% | 20.00%
Other | 17.00% | 14.00%
Defined benefit plans [member] | Actuarial assumption of expected rates of pension increases [member] | Aegon United States of America [member] | Bottom of range [member] |  |
Disclosure of sensitivity analysis for actuarial assumptions [Line Items] |  |
Equity instruments | 19.00% |
Debt instruments | 47.00% |
Other | 20.00% |
Defined benefit plans [member] | Actuarial assumption of expected rates of pension increases [member] | Aegon United States of America [member] | Top of range [member] |  |
Disclosure of sensitivity analysis for actuarial assumptions [Line Items] |  |
Equity instruments | 28.00% |
Debt instruments | 58.00% |
Other | 28.00% |

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