Segment Information - Summary of Segment Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Sales Information [Line Items]
Average Assets	$ 95,892	$ 92,143	$ 86,665
Business Banking [Member]
Sales Information [Line Items]
Average Assets	5,300	5,281	5,242
Commercial Banking [Member]
Sales Information [Line Items]
Average Assets	23,683	22,892	22,523
Commercial Real Estate [Member]
Sales Information [Line Items]
Average Assets	18,019	17,113	16,937
Discretionary Portfolio [Member]
Sales Information [Line Items]
Average Assets	22,714	20,798	18,581
Residential Mortgage Banking [Member]
Sales Information [Line Items]
Average Assets	3,512	3,333	3,157
Retail Banking [Member]
Sales Information [Line Items]
Average Assets	10,788	10,449	10,155
All Other [Member]
Sales Information [Line Items]
Average Assets	$ 11,876	$ 12,277	$ 10,070