Loans - Average Balance and Interest Income Recognized on Impaired Commercial Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 498	$ 905	$ 564	$ 966
Total interest income recognized on impaired commercial loans	2	3	3	6
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	353	624	401	660
Total interest income recognized on impaired commercial loans	1	1	2	3
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	58	127	74	127
Total interest income recognized on impaired commercial loans	0	1	0	2
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	18	66	18	90
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	69	88	71	89
Total interest income recognized on impaired commercial loans	$ 1	$ 1	$ 1	$ 1