Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Segment Reporting Information [Line Items]
Average Total Assets	$ 151,648	$ 152,669	$ 148,157
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	6,568	8,007	8,622
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	27,620	28,559	30,395
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Total Assets	22,648	25,628	26,097
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Total Assets	22,899	22,262	23,650
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	6,250	6,463	6,506
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	18,610	17,897	17,216
All Other [Member]
Segment Reporting Information [Line Items]
Average Total Assets	$ 47,053	$ 43,853	$ 35,671