Comprehensive Income (Loss) - Schedule of Components of Comprehensive Income-Gross and Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Gross
Income (loss) before federal income tax	$ 162,088	$ 145,711	$ 449,135	$ 393,502
Other comprehensive income (loss)	(337,606)	80,161	(430,540)	214,594
Comprehensive income (loss)	(175,518)	225,872	18,595	608,096
Tax
Net income	33,436	30,371	93,422	82,323
Other comprehensive income (loss)	(70,897)	16,835	(90,413)	45,065
Comprehensive income (loss)	(37,461)	47,206	3,009	127,388
Net
Net income (loss)	128,652	115,340	355,713	311,179
OCI before reclassifications			(367,572)
Reclassifications			27,445
Other comprehensive income (loss)	(266,709)	63,326	(340,127)	169,529
Comprehensive income (loss)	(138,057)	178,666	15,586	480,708
Investments Subtotal
Gross
Other comprehensive income (loss)	(338,413)	79,289	(432,960)	211,977
Tax
Other comprehensive income (loss)	(71,066)	16,653	(90,921)	44,516
Net
OCI before reclassifications			(367,572)
Reclassifications			25,533
Other comprehensive income (loss)	(267,347)	62,636	(342,039)	167,461
Net realized (gains) losses on disposals and intent-to-sell AFS securities
Gross
OCI before reclassifications	(263,272)	67,404	(358,853)	178,528
Reclassifications	5,055	580	10,036	(128)
Tax
OCI before reclassifications	(55,287)	14,156	(75,359)	37,491
Reclassifications	1,062	122	2,108	(27)
Net
OCI before reclassifications	(207,985)	53,248	(283,494)	141,037
Reclassifications	3,993	458	7,928	(101)
Other comprehensive income (loss)			(275,566)
Credit loss related
Gross
OCI before reclassifications	(93,072)	12,134	(106,428)	35,922
Reclassifications	12,876	(829)	22,285	(2,345)
Tax
OCI before reclassifications	(19,545)	2,549	(22,350)	7,544
Reclassifications	2,704	(174)	4,680	(492)
Net
OCI before reclassifications	(73,527)	9,585	(84,078)	28,378
Reclassifications	10,172	(655)	17,605	(1,853)
Other comprehensive income (loss)			(66,473)
Defined benefit pension and post-retirement life plans
Gross
Other comprehensive income (loss)	807	872	2,420	2,617
Tax
Other comprehensive income (loss)	169	182	508	549
Net
OCI before reclassifications			0
Reclassifications			1,912
Other comprehensive income (loss)	638	690	1,912	2,068
Net actuarial (gain) loss
Gross
Reclassifications	807	872	2,420	2,617
Tax
Reclassifications	169	182	508	549
Net
Reclassifications	$ 638	$ 690	$ 1,912	$ 2,068

Amount before tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

No definition available.