Loans and asset quality- Troubled Debt Restructurings (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 Contract	Dec. 31, 2012 Contract	Mar. 31, 2012 Contract
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	31	38	35
Outstanding recorded investment Pre-modification	$ 5	$ 9	$ 59
Outstanding recorded investment Post- modification	6	12	55
Domestic | Other residential mortgages
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	31	36	30
Outstanding recorded investment Pre-modification	5	8	7
Outstanding recorded investment Post- modification	6	11	8
Domestic | Wealth management loans and mortgages
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	0	2	0
Outstanding recorded investment Pre-modification	0	1	0
Outstanding recorded investment Post- modification	0	1	0
Domestic | Commercial
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	0	0	2
Outstanding recorded investment Pre-modification	0	0	38
Outstanding recorded investment Post- modification	0	0	32
Domestic | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	0	0	2
Outstanding recorded investment Pre-modification	0	0	11
Outstanding recorded investment Post- modification	0	0	12
Foreign
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	0	0	1
Outstanding recorded investment Pre-modification	0	0	3
Outstanding recorded investment Post- modification	$ 0	$ 0	$ 3