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Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) fund	Dec. 31, 2018 USD ($)
Hedge funds
Investment securities
Number of Investments Held | fund	1
Private equity funds
Investment securities
Trading security, fair value	$ 106,500,000
Number of Investments Held | fund	12
Insurance-Linked Securities Funds
Investment securities
Other long-term investments largest single investment	$ 41,200,000
Number of Investments Held	3
Cash in transit	$ 4,800,000
Unfunded Capital Commitment	10,000,000.0
1 – 3 years | Private equity funds
Investment securities
Trading security, fair value	4,800,000
3 – 5 years | Private equity funds
Investment securities
Trading security, fair value	51,900,000
5 – 10 years | Private equity funds
Investment securities
Trading security, fair value	40,200,000
10 years | Private equity funds
Investment securities
Trading security, fair value	9,600,000
Hedge funds | Hedge funds
Investment securities
Trading security, fair value	54,600,000	$ 54,300,000
Elementum Funds | Insurance-Linked Securities Funds
Investment securities
Commitment	$ 50,000,000.0
Minimum
Investment securities
Redemptions and Advanced Redemption Notice Period	30 days
Maximum
Investment securities
Redemptions and Advanced Redemption Notice Period	90 days

X

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

Number of investments held.

+ References

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- Definition

Other Long Term Investments, Cash in Transit

+ References

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- Definition

The largest investment which the entity has made in a single fund.

+ References

No definition available.

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- Definition

Redemptions and Advanced Redemption Notice Period

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- Definition

Trading Security, Fair Value

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- Definition

Unfunded Capital Commitment

+ References

No definition available.

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