Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 3,129,136	$ (757,691)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	1,081,504	6,422
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	300	(342)
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	2,045,560	(764,540)
Other invested assets
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	1,745	500
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 27	$ 269