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, 2013	Mar. 31, 2012
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	$ 615	$ 995
Total interest income recognized on impaired commercial loans	1	2
Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	445	694
Total interest income recognized on impaired commercial loans	1	1
Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	77	133
Total interest income recognized on impaired commercial loans	0	1
Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	18	78
Total interest income recognized on impaired commercial loans	0	0
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total average balance of impaired commercial loans	75	90
Total interest income recognized on impaired commercial loans	$ 0	$ 0