Loans and asset quality- Information about Past Due Loans (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	$ 105	$ 127
60-89 Days past due	10	76
>90 Days past due	14	6
Total past due	129	209
Domestic
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	105	127
60-89 Days past due	10	76
>90 Days past due	14	6
Total past due	129	209
Domestic | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	45	44
60-89 Days past due	0	0
>90 Days past due	8	0
Total past due	53	44
Domestic | Wealth management loans and mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	30	33
60-89 Days past due	4	7
>90 Days past due	0	1
Total past due	34	41
Domestic | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	0	0
60-89 Days past due	0	60
>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	29	50
60-89 Days past due	6	9
>90 Days past due	6	5
Total past due	41	64
Domestic | Financial institutions
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	1	0
60-89 Days past due	0	0
>90 Days past due	0	0
Total past due	1	0
Foreign
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days past due	0	0
60-89 Days past due	0	0
>90 Days past due	0	0
Total past due	$ 0	$ 0