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, 2025	Mar. 31, 2024
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	$ 5,305,520	$ 4,486,803
Other comprehensive income (loss) before reclassifications, net of tax	61,433	306,997
Reclassifications, net of tax	(2,586)	(1,814)
Other comprehensive income (loss)	58,847	305,183
Ending balance	5,425,416	5,039,161
Total
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(2,029,720)	(2,772,419)
Ending balance	(1,970,873)	(2,467,236)
Available for Sale Assets
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(1,319,618)	(827,596)
Other comprehensive income (loss) before reclassifications, net of tax	169,609	(239,684)
Reclassifications, net of tax	(2,639)	(1,905)
Other comprehensive income (loss)	166,970	(241,589)
Ending balance	(1,152,648)	(1,069,185)
Future Policy Benefits
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(709,042)	(1,947,391)
Other comprehensive income (loss) before reclassifications, net of tax	(110,089)	556,632
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	(110,089)	556,632
Ending balance	(819,131)	(1,390,759)
Foreign Exchange
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	(21,757)	4,719
Other comprehensive income (loss) before reclassifications, net of tax	1,913	(9,951)
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	1,913	(9,951)
Ending balance	(19,844)	(5,232)
Pension Adjustments
Increase (Decrease) in AOCI, Net of Tax
Beginning balance	20,697	(2,151)
Other comprehensive income (loss) before reclassifications, net of tax	0	0
Reclassifications, net of tax	53	91
Other comprehensive income (loss)	53	91
Ending balance	$ 20,750	$ (2,060)