Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Segment Reporting Information [Line Items]
Average Total Assets	$ 116,839	$ 116,959	$ 117,684
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	5,702	5,631	5,681
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	27,858	26,626	26,482
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Total Assets	23,572	22,885	22,811
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Total Assets	30,341	32,123	34,095
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	2,071	2,161	2,278
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	14,403	13,656	13,377
All Other [Member]
Segment Reporting Information [Line Items]
Average Total Assets	$ 12,892	$ 13,877	$ 12,960