Allowance for Credit Losses - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 1,925	$ 1,469	$ 1,736
Allowance on acquired PCD loans		99
Provision for credit losses	645	517	(75)
Net charge-offs:
Charge-offs	(570)	(303)	(338)
Recoveries	129	143	146
Net charge-offs	(441)	(160)	(192)
Ending balance	2,129	1,925	1,469
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	568	335	469
Allowance on acquired PCD loans		48
Provision for credit losses	132	244	(58)
Net charge-offs:
Charge-offs	(132)	(119)	(124)
Recoveries	52	60	48
Net charge-offs	(80)	(59)	(76)
Ending balance	620	568	335
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	611	506	607
Allowance on acquired PCD loans		49
Provision for credit losses	394	93	(25)
Net charge-offs:
Charge-offs	(253)	(60)	(100)
Recoveries	12	23	24
Net charge-offs	(241)	(37)	(76)
Ending balance	764	611	506
One-to-Four Family Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	115	72	104
Allowance on acquired PCD loans		2
Provision for credit losses	4	43	(30)
Net charge-offs:
Charge-offs	(10)	(12)	(11)
Recoveries	7	10	9
Net charge-offs	(3)	(2)	(2)
Ending balance	116	115	72
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	631	556	556
Provision for credit losses	115	137	38
Net charge-offs:
Charge-offs	(175)	(112)	(103)
Recoveries	58	50	65
Net charge-offs	(117)	(62)	(38)
Ending balance	$ 629	$ 631	$ 556