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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
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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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