Loans - Credit Risk Profile of Commercial Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Financing Receivable, Recorded Investment [Line Items]
Total	$ 42,568	$ 33,649
Total	61,452	51,867	49,600
Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	7,920	7,860
Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	12,497	10,225
Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	19,011	12,658
Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,140	2,906
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	42,568	33,649
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	7,920	7,860
Total	7,920	7,860	7,773
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	12,497	10,225
Total	12,497	10,225	9,997
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	19,011	12,658
Total	19,011	12,658	12,055
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,140	2,906
Total	3,140	2,906	1,794
Investment Grade [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	27,292	18,300
Investment Grade [Member] | Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,851	3,133
Investment Grade [Member] | Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	6,271	4,612
Investment Grade [Member] | Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	15,967	9,712
Investment Grade [Member] | Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	1,203	843
Non-Investment Grade [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	15,276	15,349
Non-Investment Grade [Member] | Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	4,069	4,727
Non-Investment Grade [Member] | Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	6,226	5,613
Non-Investment Grade [Member] | Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	3,044	2,946
Non-Investment Grade [Member] | Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	$ 1,937	$ 2,063