Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Segment Reporting Information [Line Items]
Average Assets	$ 123,252	$ 101,780	$ 95,892
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	5,424	5,339	5,300
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	24,838	24,143	23,683
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Assets	19,839	18,827	18,334
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Assets	42,509	26,648	22,714
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	2,647	2,918	3,197
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	11,568	11,035	10,788
All Other [Member]
Segment Reporting Information [Line Items]
Average Assets	$ 16,427	$ 12,870	$ 11,876