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Investment Information - Other investments (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		$ 2,043,970	$ 3,824,796
Other investable assets	[1]	0	500,000
Other investments (portion measured at fair value: $2,043,970 and $3,824,796)		2,043,970	4,324,796
Fair value option | Fixed maturities
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		414,007	843,354
Fair value option | Other investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		1,489,759	2,331,885
Fair value option | Other investments | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		528,585	1,231,731
Fair value option | Other investments | Lending
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		579,563	572,636
Fair value option | Other investments | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		56,997	90,780
Fair value option | Other investments | Energy
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		84,880	65,813
Fair value option | Other investments | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		131,910	138,646
Fair value option | Other investments | Infrastructure
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		26,359	165,516
Fair value option | Other investments | Private equity
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		81,465	48,750
Fair value option | Other investments | Real estate
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		0	18,013
Fair value option | Short-term investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		115,681	557,008
Fair value option | Equity securities
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		$ 24,523	$ 92,549
[1] Participation interests in a receivable of a reverse repurchase agreement

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