Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Segment Reporting Information [Line Items]
Average total assets	$ 204,266	$ 190,252	$ 187,395
Business Banking [Member]
Segment Reporting Information [Line Items]
Average total assets	7,968	7,597	7,515
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average total assets	49,373	40,930	39,293
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average total assets	31,878	30,599	29,982
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average total assets	50,900	42,657	40,987
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average total assets	2,746	3,986	4,370
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average total assets	21,261	20,312	20,063
All Other [Member]
Segment Reporting Information [Line Items]
Average total assets	$ 40,140	$ 44,171	$ 45,185