Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Segment Reporting Information [Line Items]
Average Assets	$ 97,345	$ 92,143	$ 89,952
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	5,321	5,281	5,287
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	24,041	22,892	22,805
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Assets	18,632	17,370	17,187
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Assets	23,153	20,798	20,306
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	3,007	3,076	3,016
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	10,912	10,449	10,348
All Other [Member]
Segment Reporting Information [Line Items]
Average Assets	$ 12,279	$ 12,277	$ 11,003