Loans and asset quality- Information about Past Due Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	$ 75	$ 127
60 to 89 days past due	10	76
Greater than 90 days past due	13	6
Total past due	98	209
Domestic
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	75	127
60 to 89 days past due	10	76
Greater than 90 days past due	13	6
Total past due	98	209
Domestic | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	28	44
60 to 89 days past due	3	0
Greater than 90 days past due	0	0
Total past due	31	44
Domestic | Wealth management loans and mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	23	33
60 to 89 days past due	3	7
Greater than 90 days past due	6	1
Total past due	32	41
Domestic | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	0	0
60 to 89 days past due	0	60
Greater than 90 days past due	0	0
Total past due	0	60
Domestic | Other residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	24	50
60 to 89 days past due	4	9
Greater than 90 days past due	7	5
Total past due	35	64
Foreign
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	0	0
60 to 89 days past due	0	0
Greater than 90 days past due	0	0
Total past due	$ 0	$ 0