Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Segment Reporting Information [Line Items]
Average Assets	$ 121,865	$ 124,340	$ 123,479
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	5,595	5,456	5,440
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	26,802	25,592	25,195
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Assets	22,875	21,131	20,116
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Assets	38,341	40,867	41,900
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	2,341	2,569	2,587
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	12,337	11,840	11,640
All Other [Member]
Segment Reporting Information [Line Items]
Average Assets	$ 13,574	$ 16,885	$ 16,601