Accumulated Other Comprehensive Loss - Changes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pre-tax Amount
Other comprehensive loss, Pre-tax Amount	$ (49,090)	$ (119,057)	$ (12,924)	$ (732,442)
Income Tax Benefit (Expense)
Other comprehensive loss, Income Tax Benefit (Expense)	13,095	31,758	3,447	195,379
Net of tax
Balance	2,359,738	2,252,611	2,269,005	2,656,912
Other comprehensive loss	(35,995)	(87,299)	(9,477)	(537,063)
Balance	2,351,009	2,200,651	2,351,009	2,200,651
Accumulated other comprehensive loss
Pre-tax Amount
Accumulated other comprehensive loss, beginning balance, Pre-tax Amount	(835,647)	(779,352)	(871,813)	(165,967)
Accumulated other comprehensive loss, ending balance, Pre-tax Amount	(884,737)	(898,409)	(884,737)	(898,409)
Income Tax Benefit (Expense)
Accumulated other comprehensive loss, beginning balance, Income Tax Benefit (Expense)	222,911	207,895	232,559	44,274
Accumulated other comprehensive loss, ending balance, Income Tax Benefit (Expense)	236,006	239,653	236,006	239,653
Net of tax
Balance	(612,736)	(571,457)	(639,254)	(121,693)
Other comprehensive loss	(35,995)	(87,299)	(9,477)	(537,063)
Balance	(648,731)	(658,756)	(648,731)	(658,756)
Pensions and Other Benefits
Net of tax
Balance	(5,431)	(24,390)	(5,431)	(24,390)
Balance	(5,431)	(24,390)	(5,431)	(24,390)
Investment securities
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount	(61,874)	(130,000)	(50,861)	(759,437)
Reclassification of net losses (gains) to net income, Pre-tax Amount	11,434	15,217	36,206	35,146
Other comprehensive loss, Pre-tax Amount	(50,440)	(114,783)	(14,655)	(724,291)
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)	16,505	34,677	13,567	202,580
Reclassification of net (losses) gains to net income, Income Tax Benefit (Expense)	(3,050)	(4,058)	(9,658)	(9,375)
Other comprehensive loss, Income Tax Benefit (Expense)	13,455	30,619	3,909	193,205
Net of tax
Unrealized net losses arising during the period, Net of tax	(45,369)	(95,323)	(37,294)	(556,857)
Reclassification of net losses to net income, Net of tax	8,384	11,159	26,548	25,771
Other comprehensive loss	(36,985)	(84,164)	(10,746)	(531,086)
Cash Flow Derivative Hedges
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount	(373)	(4,372)	(2,868)	(7,611)
Reclassification of net losses (gains) to net income, Pre-tax Amount	1,723	98	4,599	(540)
Other comprehensive loss, Pre-tax Amount	1,350	(4,274)	1,731	(8,151)
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)	100	1,165	765	2,030
Reclassification of net (losses) gains to net income, Income Tax Benefit (Expense)	(460)	(26)	(1,227)	144
Other comprehensive loss, Income Tax Benefit (Expense)	(360)	1,139	(462)	2,174
Net of tax
Balance	(4,423)	(2,842)	(4,702)
Unrealized net losses arising during the period, Net of tax	(273)	(3,207)	(2,103)	(5,581)
Reclassification of net losses to net income, Net of tax	1,263	72	3,372	(396)
Other comprehensive loss	990	(3,135)	1,269	(5,977)
Balance	$ (3,433)	$ (5,977)	$ (3,433)	$ (5,977)