Derivatives - Narrative (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) Contract	Dec. 31, 2023 USD ($) Contract
Derivative [Line Items]
Gross amounts recognized	$ 622,238,000	$ 610,920,000
Derivative liabilities - Fair value	693,548,000	613,314,000
Derivative instruments designated as hedging instruments
Derivative [Line Items]
Gross amounts recognized	15,707,000	53,815,000
Derivative liabilities - Fair value	49,616,000	13,124,000
Notional amount	5,250,000,000	5,331,480,000
Derivatives not designated as hedging instruments
Derivative [Line Items]
Gross amounts recognized	606,531,000	557,105,000
Derivative liabilities - Fair value	643,932,000	600,190,000
Notional amount	21,927,035,000	23,333,449,000
Interest rate contracts | Derivatives not designated as hedging instruments
Derivative [Line Items]
Gross amounts recognized	469,087,000	423,486,000
Derivative liabilities - Fair value	468,714,000	420,812,000
Notional amount	16,910,462,000	17,387,909,000
Interest rate contracts | Derivatives not designated as hedging instruments | LCH
Derivative [Line Items]
Gross amounts recognized	41,000,000	43,000,000
Derivative liabilities - Fair value	47,000,000	43,000,000
Interest rate contracts | Cash Flow Hedging | Derivative instruments designated as hedging instruments
Derivative [Line Items]
Gross amounts recognized	15,707,000	50,421,000
Derivative liabilities - Fair value	49,616,000	13,124,000
Notional amount	5,250,000,000	5,250,000,000
Net unrealized losses, net of tax, recorded in AOCI expected to be reclassified into earnings during next 12 months	50,000,000
Foreign exchange contracts | Derivatives not designated as hedging instruments
Derivative [Line Items]
Gross amounts recognized	60,499,000	53,678,000
Derivative liabilities - Fair value	53,153,000	42,564,000
Notional amount	$ 4,898,429,000	$ 5,827,149,000
Foreign exchange contracts | Derivatives not designated as hedging instruments | Maximum
Derivative [Line Items]
Original maturity (in years)	1 year	1 year
Credit contracts | Derivatives not designated as hedging instruments
Derivative [Line Items]
Gross amounts recognized	$ 0	$ 1,000
Derivative liabilities - Fair value	16,000	25,000
Notional amount	$ 118,144,000	$ 118,391,000
Credit contracts | Derivatives not designated as hedging instruments | RPAs
Derivative [Line Items]
Weighted average remaining maturity of outstanding RPAs	2 years 7 months 6 days	2 years 9 months 18 days
Maximum exposure of RPAs with protection sold	$ 82,000	$ 177,000
Credit contracts | Derivatives not designated as hedging instruments | Long
Derivative [Line Items]
Notional amount	$ 25,000,000	$ 25,000,000
Number of instruments held | Contract	1	1
Credit-risk-related contingent features
Derivative [Line Items]
Aggregate fair value of derivative instruments in net liability position	$ 2,000,000	$ 9,000
Collateral posted	2,000,000	$ 0
Commercial Banking | Interest rate contracts | Cash Flow Hedging | Derivative instruments designated as hedging instruments
Derivative [Line Items]
Notional amount	$ 5,300,000,000