Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive income (loss)	$ (91,149)	$ (214,920)	$ (19,473)	$ (778,762)
Income tax benefit (expense)	19,141	45,133	4,089	163,540
Other comprehensive income (loss), net of tax	(72,008)	(169,787)	(15,384)	(615,222)
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	234,396	314,267	672,382	849,597
Income tax benefit (expense)	(51,552)	(64,642)	(143,937)	(175,691)
Total reclassifications, net of tax	182,844	249,625	528,445	673,906
Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	(5,461)	(12,909)	(25,399)	(11,619)
Income tax benefit (expense)	1,147	2,711	5,334	2,440
Total reclassifications, net of tax	(4,314)	(10,198)	(20,065)	(9,179)
Accumulated other comprehensive income (loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other comprehensive income (loss), net of tax	(72,008)	(169,787)	(15,384)	(615,222)
Net unrealized gains and (losses) on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive income (loss)	(95,216)	(194,449)	(31,387)	(759,409)
Income tax benefit (expense)	19,995	40,834	6,591	159,476
Other comprehensive income (loss), net of tax	(75,221)	(153,615)	(24,796)	(599,933)
Net unrealized gains and (losses) on available-for-sale securities | Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	(3,085)	(6,681)	(13,020)	(4,273)
Income tax benefit (expense)	648	1,403	2,734	897
Total reclassifications, net of tax	(2,437)	(5,278)	(10,286)	(3,376)
Net benefit plan assets and (obligations) recognized in shareholders' equity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive income (loss)	4,067	(20,471)	11,914	(19,353)
Income tax benefit (expense)	(854)	4,299	(2,502)	4,064
Other comprehensive income (loss), net of tax	3,213	(16,172)	9,412	(15,289)
Net benefit plan assets and (obligations) recognized in shareholders' equity | Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications before tax	(2,376)	(6,228)	(12,379)	(7,346)
Income tax benefit (expense)	499	1,308	2,600	1,543
Total reclassifications, net of tax	$ (1,877)	$ (4,920)	$ (9,779)	$ (5,803)