Loans - Average Balance and Interest Income Recognized on Impaired Commercial Loans (Detail) (Commercial Loans [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 258	$ 610	$ 326	$ 612
Total interest income recognized on impaired commercial loans	2	5	9	14
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	208	443	252	444
Total interest income recognized on impaired commercial loans	2	4	9	10
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	40	62	37	69
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	0	42	16	30
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	10	63	21	69
Total interest income recognized on impaired commercial loans	$ 0	$ 1	$ 0	$ 4