Loans and asset quality- Information about Impaired Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	$ 102		$ 117		$ 135
Impaired loans without an allowance, average recorded investment	13	[1]	10	[1]	9	[1]
Total impaired loans, average recorded investment	115		127		144
Impaired loans with an allowance, interest income recognized	1		1		1
Impaired loans without an allowance, interest income recognized	0	[1]	0	[1]	0	[1]
Total impaired loans, interest income recognized	1		1		1
Impaired loans with an allowance, recorded investment	94		110
Impaired loans without an allowance, recorded investment	19	[1]	7	[1]
Total impaired loans, recorded investment	113	[2]	117	[2]
Impaired loans with an allowance, unpaid Principal balance	107		123
Impaired loans without an allowance, unpaid Principal balance	25	[1]	14	[1]
Total impaired loans, unpaid Principal balance	132	[2]	137	[2]
Impaired loans with an allowance, related allowance	20	[2],[3]	24	[2],[3]
Commercial
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	56		59		46
Impaired loans with an allowance, interest income recognized	1		1		1
Impaired loans with an allowance, recorded investment	54		57
Impaired loans with an allowance, unpaid Principal balance	58		61
Impaired loans with an allowance, related allowance	7	[3]	12	[3]
Commercial real estate
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	9		20		35
Impaired loans without an allowance, average recorded investment	8		2		3
Impaired loans with an allowance, interest income recognized	0		0		0
Impaired loans without an allowance, interest income recognized	0		0		0
Impaired loans with an allowance, recorded investment	3		15
Impaired loans without an allowance, recorded investment	13		2
Impaired loans with an allowance, unpaid Principal balance	4		16
Impaired loans without an allowance, unpaid Principal balance	13		2
Impaired loans with an allowance, related allowance	1	[3]	1	[3]
Financial institutions
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	1		1		16
Impaired loans without an allowance, average recorded investment	1		2		3
Impaired loans with an allowance, interest income recognized	0		0		0
Impaired loans without an allowance, interest income recognized	0		0		0
Impaired loans with an allowance, recorded investment	1		1
Impaired loans without an allowance, recorded investment	2		1
Impaired loans with an allowance, unpaid Principal balance	1		1
Impaired loans without an allowance, unpaid Principal balance	8		8
Impaired loans with an allowance, related allowance			0	[3]
Wealth management loans and mortgages
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	27		28		28
Impaired loans without an allowance, average recorded investment	4		6		3
Impaired loans with an allowance, interest income recognized	0		0		0
Impaired loans without an allowance, interest income recognized	0		0		0
Impaired loans with an allowance, recorded investment	27		28
Impaired loans without an allowance, recorded investment	4		4
Impaired loans with an allowance, unpaid Principal balance	27		28
Impaired loans without an allowance, unpaid Principal balance	4		4
Impaired loans with an allowance, related allowance	7	[3]	7	[3]
Foreign
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	9		9		10
Impaired loans with an allowance, interest income recognized	0		0		0
Impaired loans with an allowance, recorded investment	9		9
Impaired loans with an allowance, unpaid Principal balance	17		17
Impaired loans with an allowance, related allowance	$ 5	[3]	$ 4	[3]

[1] When the discounted cash flows, collateral value or market price equals or exceeds the carrying value of the loan, then the loan does not require an allowance under the accounting standard related to impaired loans.

[2] Excludes an aggregate of $1 million and $2 million of impaired loans in amounts individually less than $1 million at March 31, 2013 and Dec. 31, 2012, respectively. The allowance for loan loss associated with these loans totaled less than $1 million at both March 31, 2013 and Dec. 31, 2012.

[3] The allowance for impaired loans is included in the allowance for loan losses.