Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Change in Balance by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	$ 4,486,803	$ 3,949,577
Other comprehensive income (loss) before reclassifications, net of tax	306,997	(196,489)
Reclassifications, net of tax	(1,814)	25,709
Other comprehensive income (loss)	305,183	(170,780)
Ending balance	5,039,161	3,846,291
Total
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(2,772,419)	(2,790,313)
Ending balance	(2,467,236)	(2,961,093)
Available for Sale Assets
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(827,596)	(1,420,672)
Other comprehensive income (loss) before reclassifications, net of tax	(239,684)	378,162
Reclassifications, net of tax	(1,905)	25,746
Other comprehensive income (loss)	(241,589)	403,908
Ending balance	(1,069,185)	(1,016,764)
Future Policy Benefits
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(1,947,391)	(1,369,204)
Other comprehensive income (loss) before reclassifications, net of tax	556,632	(569,503)
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	556,632	(569,503)
Ending balance	(1,390,759)	(1,938,707)
Foreign Exchange
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	4,719	(1,681)
Other comprehensive income (loss) before reclassifications, net of tax	(9,951)	(5,148)
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	(9,951)	(5,148)
Ending balance	(5,232)	(6,829)
Pension Adjustments
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(2,151)	1,244
Other comprehensive income (loss) before reclassifications, net of tax	0	0
Reclassifications, net of tax	91	(37)
Other comprehensive income (loss)	91	(37)
Ending balance	$ (2,060)	$ 1,207