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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, 2023 | Dec. 31, 2022
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | $ 5,117,903 | $ 7,924,623
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (72,501) | (568,299)
Available-for-sale securities, estimated fair value, 12 months or longer | 8,111,873 | 3,356,273
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (844,824) | (393,911)
Available-for-sale securities, estimated fair value | 13,229,776 | 11,280,896
Available-for-sale securities, gross unrealized holding losses | (917,325) | (962,210)
Short-term investments, estimated fair value, less than 12 months | 1,324,927 | 774,480
Short-term investments, gross unrealized holding losses, less than 12 months | (1,526) | (58)
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 | 1,324,927 | 774,480
Short-term investments, gross unrealized holding losses | (1,526) | (58)
U.S. Treasury securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 1,072,516 | 735,605
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (17,213) | (30,583)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,956,782 | 1,907,922
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (116,329) | (107,910)
Available-for-sale securities, estimated fair value | 3,029,298 | 2,643,527
Available-for-sale securities, gross unrealized holding losses | (133,542) | (138,493)
U.S. government-sponsored enterprises [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 301,249 | 413,495
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (6,205) | (40,488)
Available-for-sale securities, estimated fair value, 12 months or longer | 628,588 | 331,391
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (100,007) | (65,591)
Available-for-sale securities, estimated fair value | 929,837 | 744,886
Available-for-sale securities, gross unrealized holding losses | (106,212) | (106,079)
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 | 1,434,351 | 2,474,289
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (18,517) | (164,537)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,929,349 | 348,943
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (201,591) | (82,694)
Available-for-sale securities, estimated fair value | 3,363,700 | 2,823,232
Available-for-sale securities, gross unrealized holding losses | (220,108) | (247,231)
Foreign governments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 359,569 | 900,322
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (12,927) | (115,324)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,005,886 | 300,423
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (138,623) | (54,399)
Available-for-sale securities, estimated fair value | 1,365,455 | 1,200,745
Available-for-sale securities, gross unrealized holding losses | (151,550) | (169,723)
Commercial mortgage-backed securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 419,295 | 1,611,603
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (12,357) | (117,482)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,634,450 | 305,217
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (165,900) | (52,186)
Available-for-sale securities, estimated fair value | 2,053,745 | 1,916,820
Available-for-sale securities, gross unrealized holding losses | (178,257) | (169,668)
Residential mortgage-backed securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 115,044 | 516,423
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (2,216) | (25,232)
Available-for-sale securities, estimated fair value, 12 months or longer | 364,356 | 9,342
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (26,557) | (1,572)
Available-for-sale securities, estimated fair value | 479,400 | 525,765
Available-for-sale securities, gross unrealized holding losses | (28,773) | (26,804)
Asset-backed securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 0 | 1,640
Available-for-sale securities, gross unrealized holding losses, less than 12 months | 0 | (53)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,204 | 0
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (37) | 0
Available-for-sale securities, estimated fair value | 1,204 | 1,640
Available-for-sale securities, gross unrealized holding losses | (37) | (53)
Corporate bonds [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 90,952 | 496,766
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (1,540) | (74,542)
Available-for-sale securities, estimated fair value, 12 months or longer | 591,258 | 153,035
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (95,780) | (29,559)
Available-for-sale securities, estimated fair value | 682,210 | 649,801
Available-for-sale securities, gross unrealized holding losses | (97,320) | (104,101)
Total fixed maturities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 3,792,976 | 7,150,143
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (70,975) | (568,241)
Available-for-sale securities, estimated fair value, 12 months or longer | 8,111,873 | 3,356,273
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (844,824) | (393,911)
Available-for-sale securities, estimated fair value | 11,904,849 | 10,506,416
Available-for-sale securities, gross unrealized holding losses | $ (915,799) | $ (962,152)

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