Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		$ 7,523	$ 6,105	$ 7,404	$ 6,155
Allowance for acquired credit losses	[1]			127
Change in accounting principle	[2]			(62)
Provision for credit losses		821	311	1,248	423
Loans charged-off		755	276	1,224	556
Less recoveries of loans charged-off		(106)	(115)	(202)	(233)
Net loan charge-offs (recoveries)		649	161	1,022	323
Balance at end of period		7,695	6,255	7,695	6,255
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		2,180	1,836	2,163	1,849
Allowance for acquired credit losses	[1]			0
Change in accounting principle	[2]			0
Provision for credit losses		119	90	183	109
Loans charged-off		110	53	173	108
Less recoveries of loans charged-off		(20)	(23)	(36)	(46)
Net loan charge-offs (recoveries)		90	30	137	62
Balance at end of period		2,209	1,896	2,209	1,896
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		1,359	1,074	1,325	1,123
Allowance for acquired credit losses	[1]			127
Change in accounting principle	[2]			0
Provision for credit losses		140	(95)	164	(149)
Loans charged-off		31	9	154	10
Less recoveries of loans charged-off		(5)	(3)	(11)	(9)
Net loan charge-offs (recoveries)		26	6	143	1
Balance at end of period		1,473	973	1,473	973
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		947	600	926	565
Allowance for acquired credit losses	[1]			0
Change in accounting principle	[2]			(31)
Provision for credit losses		66	49	117	78
Loans charged-off		121	2	125	7
Less recoveries of loans charged-off		(7)	(11)	(12)	(22)
Net loan charge-offs (recoveries)		114	(9)	113	(15)
Balance at end of period		899	658	899	658
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		925	956	970	945
Allowance for acquired credit losses	[1]			0
Change in accounting principle	[2]			(4)
Provision for credit losses		224	42	218	82
Loans charged-off		251	50	315	111
Less recoveries of loans charged-off		(31)	(34)	(60)	(66)
Net loan charge-offs (recoveries)		220	16	255	45
Balance at end of period		929	982	929	982
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		2,112	1,639	2,020	1,673
Allowance for acquired credit losses	[1]			0
Change in accounting principle	[2]			(27)
Provision for credit losses		272	225	566	303
Loans charged-off		242	162	457	320
Less recoveries of loans charged-off		(43)	(44)	(83)	(90)
Net loan charge-offs (recoveries)		199	118	374	230
Balance at end of period		$ 2,185	$ 1,746	$ 2,185	$ 1,746

[1] Represents allowance for credit deteriorated and charged-off loans acquired from MUB.

[2] Effective January 1, 2023, the Company adopted accounting guidance which removed the separate recognition and measurement of troubled debt restructurings.