Segment information - Summary of Segment Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Sales Information [Line Items]
Average Assets	$ 86,665	$ 83,662	$ 81,913
Business Banking [Member]
Sales Information [Line Items]
Average Assets	5,242	5,080	4,980
Commercial Banking [Member]
Sales Information [Line Items]
Average Assets	22,523	21,655	21,272
Commercial Real Estate [Member]
Sales Information [Line Items]
Average Assets	16,937	17,150	17,054
Discretionary Portfolio [Member]
Sales Information [Line Items]
Average Assets	18,581	16,480	16,585
Residential Mortgage Banking [Member]
Sales Information [Line Items]
Average Assets	3,157	2,858	2,847
Retail Banking [Member]
Sales Information [Line Items]
Average Assets	10,155	10,997	11,391
All Other [Member]
Sales Information [Line Items]
Average Assets	$ 10,070	$ 9,442	$ 7,784