Loans - Status of Commercial Loan Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Financing Receivable, Recorded Investment [Line Items]
Nonaccrual Loans	$ 1,790	$ 1,828
Accruing Loans Contractually Past Due 90 days or More	51	61
Total	61,452	51,867	49,600
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	41,901	32,810
Nonaccrual Loans	658	825
Accruing Loans Contractually Past Due 90 days or More	9	14
Total	42,568	33,649
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	7,468	7,244
Nonaccrual Loans	451	615
Accruing Loans Contractually Past Due 90 days or More	1	1
Total	7,920	7,860	7,773
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	12,444	10,156
Nonaccrual Loans	46	58
Accruing Loans Contractually Past Due 90 days or More	7	11
Total	12,497	10,225	9,997
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	18,869	12,521
Nonaccrual Loans	142	137
Total	19,011	12,658	12,055
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	3,120	2,889
Nonaccrual Loans	19	15
Accruing Loans Contractually Past Due 90 days or More	1	2
Total	$ 3,140	$ 2,906	$ 1,794