Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Segment Reporting Information [Line Items]
Average Total Assets	$ 187,395	$ 152,669	$ 150,967
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	7,515	8,007	8,386
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	40,464	28,559	29,109
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Total Assets	28,811	25,628	25,913
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Total Assets	40,987	22,262	22,317
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	4,370	6,463	6,582
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	20,063	17,897	17,701
All Other [Member]
Segment Reporting Information [Line Items]
Average Total Assets	$ 45,185	$ 43,853	$ 40,959