Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Segment Reporting Information [Line Items]
Average Assets	$ 123,479	$ 101,780	$ 96,750
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	5,440	5,339	5,313
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	25,195	24,143	23,997
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Assets	20,116	18,827	18,514
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Assets	41,900	26,648	23,029
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	2,587	2,918	3,090
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	11,640	11,035	10,830
All Other [Member]
Segment Reporting Information [Line Items]
Average Assets	$ 16,601	$ 12,870	$ 11,977