Investment Securities - Narrative (Details)	3 Months Ended		12 Months Ended
	Jun. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2023 USD ($) bond	Dec. 31, 2022 USD ($)	Dec. 31, 2021 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 gain			$ 126,400,000
Available-for-sale, transfer to held-to-maturity, gain (loss)			0
Held to maturity mortgage backed securities			3,729,502,000	$ 3,761,094,000
Available for sale mortgage backed securities			3,509,709,000	4,331,413,000
Held-to-maturity, interest receivable			20,600,000
Available-for-sale, interest receivable			24,700,000
Available-for-sale securities			3,152,153,000	3,852,854,000
Securities valued at less than historical cost, amount			$ 3,116,357,000
Securities valued at less than historical cost (as percent)			98.90%
Provision for credit losses, AFS			$ 9,100,000	0
Securities pledged as collateral			3,320,000,000	3,960,000,000
Realized losses			$ 20,600,000	324,000	$ 422,000
Realized gains				$ 46,000	$ 15,900,000
Income tax benefit related to security gains (losses) (as percent)			26.135%	26.135%	26.135%
Commercial Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities			$ 141,600,000	$ 149,200,000
Available for sale mortgage backed securities			710,100,000	1,070,000,000.00
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Held to maturity mortgage backed securities			1,020,000,000.00	1,040,000,000.00
Available for sale mortgage backed securities			1,230,000,000	1,470,000,000
Bonds
Debt Securities, Available-for-sale [Line Items]
Provision for credit losses, AFS			$ 7,000,000
Number of corporate bond | bond			1
Investments sold, amount			$ 247,900,000	$ 0	$ 342,600,000