Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		$ 7,404	$ 6,155
Allowance for acquired credit losses	[1]	127
Change in accounting principle	[2]	(62)
Provision for credit losses		427	112
Loans charged-off		469	280
Less recoveries of loans charged-off		(96)	(118)
Net loan charge-offs (recoveries)		373	162
Balance at end of period		7,523	6,105
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		2,163	1,849
Provision for credit losses		64	19
Loans charged-off		63	55
Less recoveries of loans charged-off		(16)	(23)
Net loan charge-offs (recoveries)		47	32
Balance at end of period		2,180	1,836
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		1,325	1,123
Allowance for acquired credit losses	[1]	127
Provision for credit losses		24	(54)
Loans charged-off		123	1
Less recoveries of loans charged-off		(6)	(6)
Net loan charge-offs (recoveries)		117	(5)
Balance at end of period		1,359	1,074
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		926	565
Change in accounting principle	[2]	(31)
Provision for credit losses		51	29
Loans charged-off		4	5
Less recoveries of loans charged-off		(5)	(11)
Net loan charge-offs (recoveries)		(1)	(6)
Balance at end of period		947	600
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		970	945
Change in accounting principle	[2]	(4)
Provision for credit losses		(6)	40
Loans charged-off		64	61
Less recoveries of loans charged-off		(29)	(32)
Net loan charge-offs (recoveries)		35	29
Balance at end of period		925	956
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		2,020	1,673
Change in accounting principle	[2]	(27)
Provision for credit losses		294	78
Loans charged-off		215	158
Less recoveries of loans charged-off		(40)	(46)
Net loan charge-offs (recoveries)		175	112
Balance at end of period		$ 2,112	$ 1,639

[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. Upon adoption, the Company reduced its allowance for credit losses and increased retained earnings net of deferred taxes through a cumulative-effect adjustment.