Acquisition of Tokio Millennium Re (Defined Benefit Pension Plan) (Details) - Pension Plan - TMR $ in Millions	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Net balance sheet liability	$ 6.5
Projected benefit obligation	20.4
Plan assets at fair value	$ 13.9

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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