Securities Securities - Amortized Cost, Allowance for Credit Losses and Estimated Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 16,767,625	$ 17,965,338
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	7,109	14,828
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,593,151	1,401,795
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	15,181,583	16,578,371
US Treasury Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	4,181,301	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	308,729	285,305
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	3,872,572	4,927,589
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	7,472,195	7,463,954
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	4,796	9,066
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,004,366	876,338
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	6,472,625	6,596,682
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,071,259	5,245,721
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2,313	5,762
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	280,056	240,152
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Securities available for sale, at estimated fair value	4,793,516	5,011,331
Other Investments [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,870	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	$ 42,870	$ 42,769