Income Taxes - Summary of Deferred Tax Assets and Liabilities from Tax Effects of Temporary Differences (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Allowance for credit losses	$ 76	$ 80
Discounts on loans acquired in a business combination	8	16
Net operating loss/tax credit carryforwards	37	38
Deferred compensation	14	12
Securities impairments	1	1
Pension and other defined benefit plans	0	2
Lease liability	36	30
Net unrealized securities losses	4	0
Other	13	14
Total	189	193
Valuation allowance	(34)	(33)
Total deferred tax assets	155	160
Loan costs	(6)	(6)
Depreciation	(11)	(12)
Prepaid expenses	(1)	(1)
Amortizable intangibles	(11)	(13)
Pension and other defined benefit plans	(4)	0
Lease financing	(33)	(32)
Mortgage servicing rights	(10)	(8)
Lease ROU asset	(34)	(28)
Net unrealized securities gains	0	(7)
Other	(2)	(2)
Total deferred tax liabilities	(112)	(109)
Net deferred tax assets	$ 43	$ 51