Loans and Leases (Allowance For Loan And Lease Losses By Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 635,737	$ 594,741	$ 594,741
Provision (benefit)	43,194	37,821
Charge-offs	(39,791)	(27,508)
Recoveries	2,302	2,987
Balance, end of period	641,442	613,914	635,737	$ 594,741
ALLL, Individually evaluated for impairment	64,995	36,049
ALLL, Collectively evaluated for impairment	576,447	577,865
Loans and leases	51,098,642		50,726,052
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, end of period			0	5,873
Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	577,663	533,125	533,125
Provision (benefit)	49,354	38,757
Charge-offs	(38,461)	(26,410)
Recoveries	553	1,574
Balance, end of period	589,109	554,750	577,663	533,125
ALLL, Individually evaluated for impairment	60,786	27,459
ALLL, Collectively evaluated for impairment	528,323	527,291
Year one	1,712,377		6,915,688
Year two	6,946,199		10,018,134
Year three	9,875,543		4,592,545
Year four	4,449,862		2,641,163
Year five	2,527,116		2,734,340
Prior	8,586,095		6,261,024
Revolving Loans Amortized Cost Basis	7,241,324		7,766,940
Loans and leases	41,338,516		40,929,834
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff	0		4,957
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	240		7,637
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	21,228		14,392
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	10,517		6,958
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	353		20,216
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff	6,123		50,349
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	38,461		104,509
Commercial Portfolio Segment [Member] | Commercial non-mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Year one	663,424		2,666,477
Year two	2,600,368		4,253,662
Year three	4,084,647		1,455,632
Year four	1,403,618		772,695
Year five	746,135		654,814
Prior	1,539,950		983,268
Revolving Loans Amortized Cost Basis	5,657,928		6,098,927
Loans and leases	16,696,070		16,885,475
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff	0		325
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	240		7,637
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	21,228		1,775
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	9,118		512
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	353		969
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff	766		4,391
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	31,705		15,609
Commercial Portfolio Segment [Member] | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, end of period			0	7,704
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	58,074	61,616	61,616
Provision (benefit)	(6,160)	(936)
Charge-offs	(1,330)	(1,098)
Recoveries	1,749	1,413
Balance, end of period	52,333	59,164	58,074	61,616
ALLL, Individually evaluated for impairment	4,209	8,590
ALLL, Collectively evaluated for impairment	48,124	$ 50,574
Year one	119,951		816,641
Year two	827,288		2,019,764
Year three	1,999,875		2,286,113
Year four	2,256,635		893,040
Year five	880,311		462,450
Prior	2,569,769		2,185,134
Revolving Loans Amortized Cost Basis	1,106,297		1,133,076
Loans and leases	9,760,126		9,796,218
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff	890		3,263
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	0		11
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	11		470
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	18		218
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	26		634
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff	385		8,107
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	1,330		12,703
Consumer Portfolio Segment [Member] | Residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Year one	112,332		742,719
Year two	755,258		1,949,928
Year three	1,931,773		2,201,633
Year four	2,174,645		843,276
Year five	832,453		441,840
Prior	2,419,693		2,048,527
Revolving Loans Amortized Cost Basis	0		0
Loans and leases	8,226,154		8,227,923
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	0		387
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	0		153
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff	64		4,630
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	64		5,170
Consumer Portfolio Segment [Member] | Home equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Year one	7,016		71,452
Year two	69,756		68,058
Year three	66,485		81,533
Year four	79,185		47,700
Year five	46,268		18,124
Prior	147,719		136,013
Revolving Loans Amortized Cost Basis	1,062,991		1,094,075
Loans and leases	1,479,420		1,516,955
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	0		4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	0		81
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	0		104
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff	177		3,114
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	177		3,303
Consumer Portfolio Segment [Member] | Consumer Loan
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Year one	603		2,470
Year two	2,274		1,778
Year three	1,617		2,947
Year four	2,805		2,064
Year five	1,590		2,486
Prior	2,357		594
Revolving Loans Amortized Cost Basis	43,306		39,001
Loans and leases	54,552		51,340
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff	890		3,263
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	0		7
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	11		2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	18		218
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	26		377
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff	144		363
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff	0		0
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	$ 1,089		4,230
Consumer Portfolio Segment [Member] | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, end of period			$ 0	$ (1,831)