Loans and Leases and the Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,638,236	$ 1,029,867	$ 1,051,071	$ 1,019,444
Provision for credit losses	150,000	45,000	725,000	122,000
Net charge-offs
Charge-offs	(52,226)	(60,241)	(211,327)	(174,747)
Recoveries	22,495	23,811	61,304	71,740
Net (charge-offs) recoveries	(29,731)	(36,430)	(150,023)	(103,007)
Ending balance	1,758,505	1,038,437	1,758,505	1,038,437
Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Net charge-offs
Adoption of new accounting standard			132,457
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	398,257	335,855	366,094	330,055
Provision for credit losses	25,450	24,538	161,444	41,146
Net charge-offs
Charge-offs	(14,434)	(15,678)	(63,425)	(40,786)
Recoveries	4,475	6,730	11,109	21,030
Net (charge-offs) recoveries	(9,959)	(8,948)	(52,316)	(19,756)
Ending balance	413,748	351,445	413,748	351,445
Commercial, Financial, Leasing, etc. [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Net charge-offs
Adoption of new accounting standard			(61,474)
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	576,321	343,296	322,201	341,655
Provision for credit losses	87,403	(16,713)	335,159	(6,415)
Net charge-offs
Charge-offs	(4,522)	(1,107)	(23,266)	(11,555)
Recoveries	2,578	1,656	4,030	3,447
Net (charge-offs) recoveries	(1,944)	549	(19,236)	(8,108)
Ending balance	661,780	327,132	661,780	327,132
Commercial Real Estate [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Net charge-offs
Adoption of new accounting standard			23,656
One-to-Four Family Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	118,921	61,011	56,033	69,125
Provision for credit losses	(683)	(309)	11,458	(5,132)
Net charge-offs
Charge-offs	(1,516)	(2,721)	(8,227)	(9,356)
Recoveries	960	1,511	4,522	4,855
Net (charge-offs) recoveries	(556)	(1,210)	(3,705)	(4,501)
Ending balance	117,682	59,492	117,682	59,492
One-to-Four Family Residential [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Net charge-offs
Adoption of new accounting standard			53,896
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	544,737	211,220	229,118	200,564
Provision for credit losses	37,830	37,735	216,939	92,212
Net charge-offs
Charge-offs	(31,754)	(40,735)	(116,409)	(113,050)
Recoveries	14,482	13,914	41,643	42,408
Net (charge-offs) recoveries	(17,272)	(26,821)	(74,766)	(70,642)
Ending balance	$ 565,295	222,134	565,295	222,134
Consumer [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Net charge-offs
Adoption of new accounting standard			194,004
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance		78,485	77,625	78,045
Provision for credit losses		(251)		189
Net charge-offs
Ending balance		$ 78,234		$ 78,234
Unallocated [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Net charge-offs
Adoption of new accounting standard			$ (77,625)