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, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 890	$ 1,093	$ 941	$ 1,118
Total interest income recognized on impaired commercial loans	8	3	14	10
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	562	703	628	745
Total interest income recognized on impaired commercial loans	5	1	8	5
Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	112	156	122	157
Total interest income recognized on impaired commercial loans	2	1	4	3
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	129	111	103	100
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	87	123	88	116
Total interest income recognized on impaired commercial loans	$ 1	$ 1	$ 2	$ 2