Loans and asset quality- Information about Impaired Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended						9 Months Ended
	Sep. 30, 2013		Jun. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	$ 51		$ 81		$ 125		$ 76		$ 131
Impaired loans without an allowance, average recorded investment	17	[1]	23	[1]	10	[1]	15	[1]	9	[1]
Total impaired loans, average recorded investment	68		104		135		91		140
Impaired loans with an allowance, interest income recognized	0		1		1		1		3
Impaired loans without an allowance, interest income recognized	0	[1]	0	[1]	0	[1]	0	[1]	0	[1]
Total impaired loans, interest income recognized	0		1		1		1		3
Impaired loans with an allowance, recorded investment	36						36				110
Impaired loans without an allowance, recorded investment	5	[1]					5	[1]			7	[1]
Total impaired loans, recorded investment	41	[2]					41	[2]			117	[2]
Impaired loans with an allowance, unpaid Principal balance	49						49				123
Impaired loans without an allowance, unpaid Principal balance	12	[1]					12	[1]			14	[1]
Total impaired loans, unpaid Principal balance	61	[2]					61	[2]			137	[2]
Impaired loans with an allowance, related allowance	11	[2],[3]					11	[2],[3]			24	[2],[3]
Commercial
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	30		50		61		43		53
Impaired loans without an allowance, average recorded investment	4		4		0		2		0
Impaired loans with an allowance, interest income recognized	0		1		1		1		3
Impaired loans without an allowance, interest income recognized	0		0		0		0		0
Impaired loans with an allowance, recorded investment	15						15				57
Impaired loans without an allowance, recorded investment	0						0				0
Impaired loans with an allowance, unpaid Principal balance	19						19				61
Impaired loans without an allowance, unpaid Principal balance	0						0				0
Impaired loans with an allowance, related allowance	3	[3]					3	[3]			12	[3]
Commercial real estate
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	2		2		26		6		31
Impaired loans without an allowance, average recorded investment	7		13		2		7		3
Impaired loans with an allowance, interest income recognized	0		0		0		0		0
Impaired loans without an allowance, interest income recognized	0		0		0		0		0
Impaired loans with an allowance, recorded investment	2						2				15
Impaired loans without an allowance, recorded investment	1						1				2
Impaired loans with an allowance, unpaid Principal balance	3						3				16
Impaired loans without an allowance, unpaid Principal balance	2						2				2
Impaired loans with an allowance, related allowance	1	[3]					1	[3]			1	[3]
Financial institutions
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	0		1		1		0		9
Impaired loans without an allowance, average recorded investment	2		2		2		2		2
Impaired loans with an allowance, interest income recognized	0		0		0		0		0
Impaired loans without an allowance, interest income recognized	0		0		0		0		0
Impaired loans with an allowance, recorded investment	0						0				1
Impaired loans without an allowance, recorded investment	1						1				1
Impaired loans with an allowance, unpaid Principal balance	0						0				1
Impaired loans without an allowance, unpaid Principal balance	7						7				8
Impaired loans with an allowance, related allowance	0	[3]					0	[3]			0	[3]
Wealth management loans and mortgages
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	10		19		28		18		28
Impaired loans without an allowance, average recorded investment	4		4		6		4		4
Impaired loans with an allowance, interest income recognized	0		0		0		0		0
Impaired loans without an allowance, interest income recognized	0		0		0		0		0
Impaired loans with an allowance, recorded investment	10						10				28
Impaired loans without an allowance, recorded investment	3						3				4
Impaired loans with an allowance, unpaid Principal balance	10						10				28
Impaired loans without an allowance, unpaid Principal balance	3						3				4
Impaired loans with an allowance, related allowance	3	[3]					3	[3]			7	[3]
Foreign
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	9		9		9		9		10
Impaired loans with an allowance, interest income recognized	0		0		0		0		0
Impaired loans with an allowance, recorded investment	9						9				9
Impaired loans with an allowance, unpaid Principal balance	17						17				17
Impaired loans with an allowance, related allowance	$ 4	[3]					$ 4	[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 Sept. 30, 2013 and Dec. 31, 2012, respectively. The allowance for loan loss associated with these loans totaled less than $1 million at both Sept. 30, 2013 and Dec. 31, 2012.

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