Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 16,449,841	$ 17,965,338
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	31,251	14,828
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,161,049	1,401,795
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	15,320,043	16,578,371
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	4,188,623	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	200,877	285,305
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	3,987,746	4,927,589
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	7,418,797	7,463,954
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	22,023	9,066
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	748,157	876,338
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	6,692,663	6,596,682
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	4,799,347	5,245,721
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	9,228	5,762
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	212,015	240,152
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	4,596,560	5,011,331
Other Investments [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	43,074	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	$ 43,074	$ 42,769