Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Segment Reporting Information [Line Items]
Average Assets	$ 122,978	$ 124,340	$ 123,252
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	5,596	5,456	5,424
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	26,723	25,592	24,838
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Assets	22,977	21,131	19,839
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Assets	38,731	40,867	42,509
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	2,426	2,569	2,647
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	12,204	11,840	11,568
All Other [Member]
Segment Reporting Information [Line Items]
Average Assets	$ 14,321	$ 16,885	$ 16,427