Loans - Average Balance and Interest Income Recognized on Impaired Commercial Loans (Detail) (Commercial Loan [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 397	$ 615
Total interest income recognized on impaired commercial loans	6	4
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	297	445
Total interest income recognized on impaired commercial loans	6	3
Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	35	77
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	33	18
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	32	75
Total interest income recognized on impaired commercial loans	$ 0	$ 1