Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Segment Reporting Information [Line Items]
Average Total Assets	$ 117,021	$ 120,860	$ 121,865
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	5,656	5,602	5,595
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	26,542	26,573	26,802
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Total Assets	22,848	22,741	22,875
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Total Assets	33,277	37,203	38,341
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	2,186	2,355	2,341
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Total Assets	13,403	12,702	12,337
All Other [Member]
Segment Reporting Information [Line Items]
Average Total Assets	$ 13,109	$ 13,684	$ 13,574