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Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$ 6,099,189	$ 1,467,268
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(35,984)	(10,821)
Available-for-sale securities, estimated fair value, 12 months or longer	8,807,311	8,515,061
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(737,141)	(650,461)
Available-for-sale securities, estimated fair value	14,906,500	9,982,329
Available-for-sale securities, gross unrealized holding losses	(773,125)	(661,282)
Short-term investments, estimated fair value, less than 12 months	2,548,368	52,601
Short-term investments, gross unrealized holding losses, less than 12 months	(1,409)	(393)
Short-term investments, estimated fair value, 12 months or longer	0	0
Short-term investments, gross unrealized holding losses, 12 months or longer	0	0
Short-term investments, estimated fair value	2,548,368	52,601
Short-term investments, gross unrealized holding losses	(1,409)	(393)
U.S. Treasury securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	1,851,326	317,027
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(13,288)	(2,147)
Available-for-sale securities, estimated fair value, 12 months or longer	1,626,173	1,507,784
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(70,006)	(60,257)
Available-for-sale securities, estimated fair value	3,477,499	1,824,811
Available-for-sale securities, gross unrealized holding losses	(83,294)	(62,404)
U.S. government-sponsored enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	175,742	145,143
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(1,717)	(2,134)
Available-for-sale securities, estimated fair value, 12 months or longer	842,483	723,537
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(101,618)	(87,770)
Available-for-sale securities, estimated fair value	1,018,225	868,680
Available-for-sale securities, gross unrealized holding losses	(103,335)	(89,904)
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	644,166	679,124
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(6,282)	(3,881)
Available-for-sale securities, estimated fair value, 12 months or longer	2,663,971	2,332,281
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(208,208)	(177,697)
Available-for-sale securities, estimated fair value	3,308,137	3,011,405
Available-for-sale securities, gross unrealized holding losses	(214,490)	(181,578)
Foreign governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	421,032	49,056
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(6,875)	(128)
Available-for-sale securities, estimated fair value, 12 months or longer	1,019,706	1,113,616
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(131,583)	(96,746)
Available-for-sale securities, estimated fair value	1,440,738	1,162,672
Available-for-sale securities, gross unrealized holding losses	(138,458)	(96,874)
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	246,505	169,557
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(1,957)	(1,792)
Available-for-sale securities, estimated fair value, 12 months or longer	1,706,126	1,790,637
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(127,377)	(134,561)
Available-for-sale securities, estimated fair value	1,952,631	1,960,194
Available-for-sale securities, gross unrealized holding losses	(129,334)	(136,353)
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	25,119	20,420
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(603)	(80)
Available-for-sale securities, estimated fair value, 12 months or longer	373,828	431,705
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(21,044)	(21,781)
Available-for-sale securities, estimated fair value	398,947	452,125
Available-for-sale securities, gross unrealized holding losses	(21,647)	(21,861)
Corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	186,931	34,340
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(3,853)	(266)
Available-for-sale securities, estimated fair value, 12 months or longer	575,024	615,501
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(77,305)	(71,649)
Available-for-sale securities, estimated fair value	761,955	649,841
Available-for-sale securities, gross unrealized holding losses	(81,158)	(71,915)
Total fixed maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	3,550,821	1,414,667
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(34,575)	(10,428)
Available-for-sale securities, estimated fair value, 12 months or longer	8,807,311	8,515,061
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(737,141)	(650,461)
Available-for-sale securities, estimated fair value	12,358,132	9,929,728
Available-for-sale securities, gross unrealized holding losses	$ (771,716)	$ (660,889)

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