Investment Securities - Narrative (Details)	3 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($) bond	Jun. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, transfer to held-to-maturity			$ 1,990,000,000	$ 500,800,000
Debt securities, held-to-maturity transfer, unrealized loss	$ 121,900,000
Available-for-sale, transfer to held-to-maturity, gain (loss)	0
Held to maturity mortgage backed securities	3,710,472,000				$ 3,729,502,000
Available for sale mortgage backed securities	3,394,971,000				3,509,709,000
Held-to-maturity, interest receivable	25,600,000
Available-for-sale, interest receivable	17,400,000
Available-for-sale securities	3,027,558,000				3,152,153,000
Securities valued at less than historical cost, amount	$ 2,973,613,000
Securities valued at less than historical cost (as percent)	98.20%
Provision for credit loss expense	$ 0	$ 12,800,000
Securities charged-off		7,000,000
Securities pledged as collateral	2,910,000,000				3,320,000,000
Realized gains	0	0
Realized losses	$ 0	$ 0
Income tax benefit related to security gains (losses) (as percent)	26.135%	26.135%
Commercial Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	$ 140,600,000				141,600,000
Available for sale mortgage backed securities	665,100,000				710,100,000
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities	1,000,000,000				1,020,000,000.00
Available for sale mortgage backed securities	$ 1,180,000,000				$ 1,230,000,000
Bonds
Debt Securities, Available-for-sale [Line Items]
Number of uncollectible bonds | bond		1