Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (836,964)	$ (3,375,764)	$ 2,292,172	$ (4,133,455)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(25,759)	8,668	1,055,745	15,090
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(758)	(1,394)	(458)	(1,736)
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(812,224)	(3,386,059)	1,233,336	(4,150,599)
Other invested assets
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	1,823	970	3,568	1,470
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (46)	$ 2,051	$ (19)	$ 2,320