Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Segment Reporting Information [Line Items]
Average Total Assets	$ 117,667	$ 116,959	$ 117,021
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	5,724	5,631	5,656
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	27,981	26,626	26,542
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Total Assets	23,720	22,885	22,848
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Total Assets	29,888	32,123	33,277
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	2,173	2,161	2,186
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	14,580	13,656	13,403
All Other [Member]
Segment Reporting Information [Line Items]
Average Total Assets	$ 13,601	$ 13,877	$ 13,109