v3.26.3
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
Sep. 30, 2026
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months $ 12,636,357 $ 946,645
Available-for-sale securities, gross unrealized holding losses, less than 12 months (382,305) (4,061)
Available-for-sale securities, estimated fair value, 12 months or longer 5,633,989 6,816,461
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (537,817) (327,375)
Available-for-sale securities, estimated fair value 18,270,346 7,763,106
Available-for-sale securities, gross unrealized holding losses (920,122) (331,436)
U.S. Treasury securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 4,389,125 197,135
Available-for-sale securities, gross unrealized holding losses, less than 12 months (113,882) (470)
Available-for-sale securities, estimated fair value, 12 months or longer 986,030 1,275,453
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (44,722) (13,171)
Available-for-sale securities, estimated fair value 5,375,155 1,472,588
Available-for-sale securities, gross unrealized holding losses (158,604) (13,641)
U.S. government-sponsored enterprises [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 789,093 108,490
Available-for-sale securities, gross unrealized holding losses, less than 12 months (32,862) (112)
Available-for-sale securities, estimated fair value, 12 months or longer 722,508 802,349
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (89,701) (57,631)
Available-for-sale securities, estimated fair value 1,511,601 910,839
Available-for-sale securities, gross unrealized holding losses (122,563) (57,743)
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 1,754,504 184,124
Available-for-sale securities, gross unrealized holding losses, less than 12 months (83,762) (970)
Available-for-sale securities, estimated fair value, 12 months or longer 1,455,084 1,871,154
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (161,099) (104,587)
Available-for-sale securities, estimated fair value 3,209,588 2,055,278
Available-for-sale securities, gross unrealized holding losses (244,861) (105,557)
Foreign governments, agencies and supranationals [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 1,491,510 214,787
Available-for-sale securities, gross unrealized holding losses, less than 12 months (68,271) (1,008)
Available-for-sale securities, estimated fair value, 12 months or longer 1,038,467 1,181,298
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (121,774) (72,686)
Available-for-sale securities, estimated fair value 2,529,977 1,396,085
Available-for-sale securities, gross unrealized holding losses (190,045) (73,694)
Agency mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 1,662,303 156,553
Available-for-sale securities, gross unrealized holding losses, less than 12 months (78,033) (701)
Available-for-sale securities, estimated fair value, 12 months or longer 1,230,123 1,446,048
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (88,580) (58,840)
Available-for-sale securities, estimated fair value 2,892,426 1,602,601
Available-for-sale securities, gross unrealized holding losses (166,613) (59,541)
Non-agency mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 5,760 5,889
Available-for-sale securities, gross unrealized holding losses, less than 12 months (102) (6)
Available-for-sale securities, estimated fair value, 12 months or longer 37,502 59,869
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (872) (532)
Available-for-sale securities, estimated fair value 43,262 65,758
Available-for-sale securities, gross unrealized holding losses (974) (538)
Corporate and university bonds [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 6,626 20,488
Available-for-sale securities, gross unrealized holding losses, less than 12 months (272) (174)
Available-for-sale securities, estimated fair value, 12 months or longer 164,275 180,290
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (31,069) (19,928)
Available-for-sale securities, estimated fair value 170,901 200,778
Available-for-sale securities, gross unrealized holding losses (31,341) (20,102)
Total fixed maturity securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 10,098,921 887,466
Available-for-sale securities, gross unrealized holding losses, less than 12 months (377,184) (3,441)
Available-for-sale securities, estimated fair value, 12 months or longer 5,633,989 6,816,461
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (537,817) (327,375)
Available-for-sale securities, estimated fair value 15,732,910 7,703,927
Available-for-sale securities, gross unrealized holding losses (915,001) (330,816)
Short-term investments [Member]    
Debt Securities, Available-for-sale [Line Items]    
Short-term investments, estimated fair value, less than 12 months 2,537,436 59,179
Short-term investments, gross unrealized holding losses, less than 12 months (5,121) (620)
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 2,537,436 59,179
Short-term investments, gross unrealized holding losses $ (5,121) $ (620)