Loans and leases and allowance for credit losses - Loan and Leases Considered Nonaccrual and Interest Income Recognized on Loans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	$ 1,163	$ 986	$ 997
Amortized Cost without Allowance	527	1,180	1,442
Nonaccrual	1,690	2,166	2,439	$ 2,060
Amortized Cost	1,690	2,166	2,439	2,060
Interest Income Recognized	92	78	77
Commercial Portfolio Segment
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	516	397	212
Amortized Cost without Allowance	180	273	292
Nonaccrual	696	670	504	371
Amortized Cost	696	670	504	371
Interest Income Recognized	23	22	26
Commercial Real Estate | Commercial
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	328	288	366
Amortized Cost without Allowance	140	581	874
Nonaccrual	468	869	1,240	919
Amortized Cost	468	869	1,240	919
Interest Income Recognized	43	29	14
Commercial Real Estate | Residential builder and developer
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	2	3	1
Amortized Cost without Allowance	0	0	0
Nonaccrual	2	3	1	3
Amortized Cost	2	3	1	3
Interest Income Recognized	1	0	2
Commercial Real Estate | Other commercial construction
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	60	71	59
Amortized Cost without Allowance	6	100	66
Nonaccrual	66	171	125	111
Amortized Cost	66	171	125	111
Interest Income Recognized	4	2	4
Residential Real Estate | Residential
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	137	100	195
Amortized Cost without Allowance	142	170	155
Nonaccrual	279	270	350	479
Amortized Cost	279	270	350	479
Interest Income Recognized	15	17	26
Consumer: | Home equity lines and loans
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	36	42	43
Amortized Cost without Allowance	45	39	42
Nonaccrual	81	81	85	70
Amortized Cost	81	81	85	70
Interest Income Recognized	6	7	4
Consumer: | Recreational finance
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	21	24	37
Amortized Cost without Allowance	10	12	8
Nonaccrual	31	36	45	28
Amortized Cost	31	36	45	28
Interest Income Recognized	0	1	1
Consumer: | Automobile
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	9	9	35
Amortized Cost without Allowance	3	5	5
Nonaccrual	12	14	40	34
Amortized Cost	12	14	40	34
Interest Income Recognized	0	0	0
Consumer: | Other
Certain Loans Acquired in Transfer Accounted for as Debt Securities Accretable Yield Movement Schedule [Line Items]
Amortized Cost with Allowance	54	52	49
Amortized Cost without Allowance	1	0	0
Nonaccrual	55	52	49	45
Amortized Cost	55	52	49	$ 45
Interest Income Recognized	$ 0	$ 0	$ 0