Loans - Average Balance and Interest Income Recognized on Impaired Commercial Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 610	$ 890	$ 612	$ 941
Total interest income recognized on impaired commercial loans	5	8	14	14
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	443	562	444	628
Total interest income recognized on impaired commercial loans	4	5	10	8
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	62	112	69	122
Total interest income recognized on impaired commercial loans	0	2	0	4
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	42	129	30	103
Total interest income recognized on impaired commercial loans	0	0	0	0
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	63	87	69	88
Total interest income recognized on impaired commercial loans	$ 1	$ 1	$ 4	$ 2