Investment Securities - Narrative (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2023 USD ($) investment_security	Dec. 31, 2023 USD ($) investment_security	Dec. 31, 2022 USD ($) investment_security	Dec. 31, 2021 USD ($)
Summary of Investment Holdings [Line Items]
Transfers of investment securities from available-for-sale to held-to-maturity		$ 360,347,000	$ 1,019,472,000	$ 319,924,000
Accumulated other comprehensive loss, net of tax	$ (99,625,000)	(99,625,000)	(265,247,000)
Proceeds from sales of securities available-for-sale		1,568,604,000	936,413,000	901,137,000
Investments held-to-maturity, allowance for credit losses	126,000	126,000	43,000	$ 22,000
Allowance for credit losses on debt securities, available-for-sale	$ 0	0	0
Available-for-sale securities, provision for credit losses		$ 0	$ 0
Available-for-sale and held-to-maturity securities in nonaccrual status | investment_security	0	0	0
Available-for-sale and held-to-maturity securities purchased with deterioration in credit quality | investment_security	0	0	0
Available-for-sale and held-to-maturity collateral dependent | investment_security	0	0	0
FHLB stock	$ 19,400,000	$ 19,400,000	$ 27,700,000
FRB stock	75,200,000	75,200,000	74,800,000
Other stock	4,700,000	4,700,000	17,400,000
Impairment loss on investments in FHLB, FRB and other stock		0
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Summary of Investment Holdings [Line Items]
Accumulated other comprehensive income (loss) before tax	(36,000,000)	(36,000,000)	(303,700,000)
Accumulated other comprehensive loss, net of tax	(25,800,000)	(25,800,000)	(217,400,000)
Other comprehensive income (loss), net of tax	(182,300,000)
Asset Pledged as Collateral
Summary of Investment Holdings [Line Items]
Investments	2,800,000,000	2,800,000,000	195,600,000
Asset Pledged as Collateral | Federal Reserve Discount Window
Summary of Investment Holdings [Line Items]
Investments	1,410,000,000	1,410,000,000
Asset Pledged as Collateral | Federal Reserves New Bank Term Funding Program
Summary of Investment Holdings [Line Items]
Investments	1,190,000,000	1,190,000,000
Municipal bonds
Summary of Investment Holdings [Line Items]
Securities transferred from available-for-sale to held-to-maturity			831,400,000
Transfers of investment securities from available-for-sale to held-to-maturity			780,700,000
Debt securities, held-to-maturity, transfer, unrealized loss			50,800,000
Accumulated other comprehensive income (loss) before tax	(102,900,000)	(102,900,000)	(66,900,000)
Accumulated other comprehensive loss, net of tax	(73,900,000)	(73,900,000)	(47,900,000)
Investments held-to-maturity, allowance for credit losses	126,000	126,000	43,000
Mortgage-backed securities
Summary of Investment Holdings [Line Items]
Securities transferred from available-for-sale to held-to-maturity		410,700,000	255,000,000
Transfers of investment securities from available-for-sale to held-to-maturity		360,300,000	238,800,000
Debt securities, held-to-maturity, transfer, unrealized loss		50,400,000	16,200,000
Investments held-to-maturity, allowance for credit losses	$ 0	$ 0	$ 0
U.S. Treasury, U.S. Government Agency, And U.S. Government-Sponsored Enterprise Securities
Summary of Investment Holdings [Line Items]
Percentage of total debt securities, available for sale	61.00%	61.00%
Lower Yielding AFS Securities | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Summary of Investment Holdings [Line Items]
Proceeds from sales of securities available-for-sale	$ 1,260,000,000
Other comprehensive income (loss) before tax	$ (254,100,000)