Investments - Schedule of Unrealized Investment Losses by Class of Investment (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	$ 2,062,574	$ 3,886,032
Unrealized Loss, Less than Twelve Months	(67,283)	(183,665)
Fair Value, Twelve Months or Longer	8,439,128	8,001,246
Unrealized Loss, Twelve Months or Longer	(1,570,524)	(1,741,324)
Fair Value	10,501,702	11,887,278
Unrealized Loss	(1,637,807)	(1,924,989)
Investment grade securities:
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	2,015,800	3,809,580
Unrealized Loss, Less than Twelve Months	(60,556)	(179,843)
Fair Value, Twelve Months or Longer	8,156,383	7,705,596
Unrealized Loss, Twelve Months or Longer	(1,520,289)	(1,671,119)
Fair Value	10,172,183	11,515,176
Unrealized Loss	(1,580,845)	(1,850,962)
Investment grade securities: | U.S. Government direct, guaranteed, and government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	4,894	11,268
Unrealized Loss, Less than Twelve Months	(454)	(290)
Fair Value, Twelve Months or Longer	368,750	347,527
Unrealized Loss, Twelve Months or Longer	(25,024)	(42,504)
Fair Value	373,644	358,795
Unrealized Loss	(25,478)	(42,794)
Investment grade securities: | States, municipalities, and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	535,186	778,244
Unrealized Loss, Less than Twelve Months	(12,491)	(32,894)
Fair Value, Twelve Months or Longer	1,731,104	1,532,264
Unrealized Loss, Twelve Months or Longer	(519,061)	(501,865)
Fair Value	2,266,290	2,310,508
Unrealized Loss	(531,552)	(534,759)
Investment grade securities: | Foreign governments
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	5,616	0
Unrealized Loss, Less than Twelve Months	(26)	0
Fair Value, Twelve Months or Longer	25,370	24,925
Unrealized Loss, Twelve Months or Longer	(8,014)	(8,870)
Fair Value	30,986	24,925
Unrealized Loss	(8,040)	(8,870)
Investment grade securities: | Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	1,451,887	2,996,837
Unrealized Loss, Less than Twelve Months	(47,523)	(146,564)
Fair Value, Twelve Months or Longer	6,029,780	5,758,241
Unrealized Loss, Twelve Months or Longer	(968,140)	(1,115,789)
Fair Value	7,481,667	8,755,078
Unrealized Loss	(1,015,663)	(1,262,353)
Investment grade securities: | Corporates | Industrials
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	680,126	1,487,940
Unrealized Loss, Less than Twelve Months	(14,131)	(73,404)
Fair Value, Twelve Months or Longer	3,667,956	3,433,034
Unrealized Loss, Twelve Months or Longer	(591,006)	(690,920)
Fair Value	4,348,082	4,920,974
Unrealized Loss	(605,137)	(764,324)
Investment grade securities: | Corporates | Financial
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	469,436	961,932
Unrealized Loss, Less than Twelve Months	(29,118)	(52,946)
Fair Value, Twelve Months or Longer	1,806,739	1,785,130
Unrealized Loss, Twelve Months or Longer	(294,440)	(333,873)
Fair Value	2,276,175	2,747,062
Unrealized Loss	(323,558)	(386,819)
Investment grade securities: | Corporates | Utilities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	302,325	546,965
Unrealized Loss, Less than Twelve Months	(4,274)	(20,214)
Fair Value, Twelve Months or Longer	555,085	540,077
Unrealized Loss, Twelve Months or Longer	(82,694)	(90,996)
Fair Value	857,410	1,087,042
Unrealized Loss	(86,968)	(111,210)
Investment grade securities: | Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	18,217	23,231
Unrealized Loss, Less than Twelve Months	(62)	(95)
Fair Value, Twelve Months or Longer	1,379	42,639
Unrealized Loss, Twelve Months or Longer	(50)	(2,091)
Fair Value	19,596	65,870
Unrealized Loss	(112)	(2,186)
Below investment grade securities:
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	46,774	76,452
Unrealized Loss, Less than Twelve Months	(6,727)	(3,822)
Fair Value, Twelve Months or Longer	282,745	295,650
Unrealized Loss, Twelve Months or Longer	(50,235)	(70,205)
Fair Value	329,519	372,102
Unrealized Loss	(56,962)	(74,027)
Below investment grade securities: | States, municipalities, and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	0	0
Unrealized Loss, Less than Twelve Months	0	0
Fair Value, Twelve Months or Longer	1,751	0
Unrealized Loss, Twelve Months or Longer	(210)	0
Fair Value	1,751	0
Unrealized Loss	(210)	0
Below investment grade securities: | Corporates
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	46,774	76,452
Unrealized Loss, Less than Twelve Months	(6,727)	(3,822)
Fair Value, Twelve Months or Longer	280,994	293,452
Unrealized Loss, Twelve Months or Longer	(50,025)	(70,205)
Fair Value	327,768	369,904
Unrealized Loss	(56,752)	(74,027)
Below investment grade securities: | Corporates | Industrials
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	35,564	54,199
Unrealized Loss, Less than Twelve Months	(6,631)	(2,656)
Fair Value, Twelve Months or Longer	141,446	142,638
Unrealized Loss, Twelve Months or Longer	(33,595)	(38,350)
Fair Value	177,010	196,837
Unrealized Loss	(40,226)	(41,006)
Below investment grade securities: | Corporates | Financial
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	6,185	2,990
Unrealized Loss, Less than Twelve Months	(36)	(53)
Fair Value, Twelve Months or Longer	101,427	126,811
Unrealized Loss, Twelve Months or Longer	(10,372)	(26,171)
Fair Value	107,612	129,801
Unrealized Loss	(10,408)	(26,224)
Below investment grade securities: | Corporates | Utilities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	5,025	19,263
Unrealized Loss, Less than Twelve Months	(60)	(1,113)
Fair Value, Twelve Months or Longer	38,121	24,003
Unrealized Loss, Twelve Months or Longer	(6,058)	(5,684)
Fair Value	43,146	43,266
Unrealized Loss	(6,118)	(6,797)
Below investment grade securities: | Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than Twelve Months	0	0
Unrealized Loss, Less than Twelve Months	0	0
Fair Value, Twelve Months or Longer	0	2,198
Unrealized Loss, Twelve Months or Longer	0	0
Fair Value	0	2,198
Unrealized Loss	$ 0	$ 0