Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (245,974)	$ (537,267)	$ (4,379,429)	$ (2,773,701)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	72	(1,199)	15,162	(4,898)
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(753)	950	(2,489)	(292)
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(246,742)	(537,079)	(4,397,341)	(2,768,959)
Other invested assets
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	1,405	0	2,875	0
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 44	$ 61	$ 2,364	$ 448