Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 16,825,791	$ 17,965,338
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	5,156	14,828
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,633,309	1,401,795
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	15,197,638	16,578,371
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	4,184,938	5,212,894
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	302,607	285,305
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	3,882,331	4,927,589
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	7,567,795	7,463,954
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2,840	9,066
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,033,208	876,338
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	6,537,427	6,596,682
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,030,087	5,245,721
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2,316	5,762
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	297,494	240,152
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	4,734,909	5,011,331
Other Investments [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,971	42,769
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	$ 42,971	$ 42,769