Liability For Future Policy Benefits (Additional Insurance Reserves) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Insurance [Abstract]
Balance, including amounts in AOCI, post-flooring	$ 14,280,793	$ 12,664,445
Flooring impact and amounts in AOCI	831,583	1,269,237
Balance, excluding amounts in AOCI, beginning of period, pre-flooring	15,112,376	13,933,682
Effect of actual variances from expected experience and other activity			$ 141,303	$ (32,188)
Adjusted balance, beginning of period			$ 15,253,679	$ 13,901,494
Assessments collected	297,419	267,869
Interest accrual	128,241	117,307
Benefits paid	(68,233)	(71,551)
Balance, excluding amounts in AOCI, end of period, pre-flooring	15,611,106	14,215,119
Flooring impact and amounts in AOCI	(1,014,852)	(962,417)
Balance, including amounts in AOCI, end of period, post-flooring	14,596,254	13,252,702
Less: Reinsurance recoverables	14,416,881	13,029,847
Balance after reinsurance recoverables, including amounts in AOCI, end of period	179,373	222,855
Gross assessments	$ 419,396	$ 427,489
Weighted-average duration of the liability in years (at original discount rate)	22 years	22 years
Weighted-average interest rate (at original discount rate)	3.39%	3.38%