Loans and asset quality- Information about Impaired Loans (Detail) (USD $)	3 Months Ended						9 Months Ended
	Sep. 30, 2014		Jun. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	$ 25,000,000		$ 29,000,000		$ 51,000,000		$ 28,000,000		$ 76,000,000
Impaired loans without an allowance, average recorded investment	3,000,000	[1]	3,000,000	[1]	17,000,000	[1]	3,000,000	[1]	15,000,000	[1]
Total impaired loans, average recorded investment	28,000,000		32,000,000		68,000,000		31,000,000		91,000,000
Impaired loans with an allowance, interest income recognized	0		0		0		0		1,000,000
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		0		0		0		1,000,000
Impaired loans with an allowance, recorded investment	22,000,000						22,000,000				32,000,000
Impaired loans without an allowance, recorded investment	3,000,000	[1]					3,000,000	[1]			4,000,000	[1]
Total impaired loans, recorded investment	25,000,000	[2]					25,000,000	[2]			36,000,000	[2]
Impaired loans with an allowance, unpaid Principal balance	24,000,000						24,000,000				50,000,000
Impaired loans without an allowance, unpaid Principal balance	3,000,000	[1]					3,000,000	[1]			4,000,000	[1]
Total impaired loans, unpaid Principal balance	27,000,000	[2]					27,000,000	[2]			54,000,000	[2]
Impaired loans with an allowance, related allowance	6,000,000	[2],[3]					6,000,000	[2],[3]			7,000,000	[2],[3]
Commercial
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	13,000,000		13,000,000		30,000,000		14,000,000		43,000,000
Impaired loans without an allowance, average recorded investment	0		0		4,000,000		0		2,000,000
Impaired loans with an allowance, interest income recognized	0		0		0		0		1,000,000
Impaired loans without an allowance, interest income recognized	0		0		0		0		0
Impaired loans with an allowance, recorded investment	13,000,000						13,000,000				15,000,000
Impaired loans with an allowance, unpaid Principal balance	13,000,000						13,000,000				20,000,000
Impaired loans with an allowance, related allowance	4,000,000	[3]					4,000,000	[3]			2,000,000	[3]
Commercial real estate
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	3,000,000		2,000,000		2,000,000		2,000,000		6,000,000
Impaired loans without an allowance, average recorded investment	1,000,000		1,000,000		7,000,000		1,000,000		7,000,000
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	2,000,000						2,000,000				2,000,000
Impaired loans without an allowance, recorded investment	1,000,000						1,000,000				1,000,000
Impaired loans with an allowance, unpaid Principal balance	3,000,000						3,000,000				4,000,000
Impaired loans without an allowance, unpaid Principal balance	1,000,000						1,000,000				1,000,000
Impaired loans with an allowance, related allowance	1,000,000	[3]					1,000,000	[3]			1,000,000	[3]
Financial institutions
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	0		0		0		0		0
Impaired loans without an allowance, average recorded investment	0		0		2,000,000		0		2,000,000
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				0
Impaired loans with an allowance, unpaid Principal balance	0						0				0
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	7,000,000		8,000,000		10,000,000		8,000,000		18,000,000
Impaired loans without an allowance, average recorded investment	2,000,000		2,000,000		4,000,000		2,000,000		4,000,000
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	7,000,000						7,000,000				9,000,000
Impaired loans without an allowance, recorded investment	2,000,000						2,000,000				3,000,000
Impaired loans with an allowance, unpaid Principal balance	8,000,000						8,000,000				9,000,000
Impaired loans without an allowance, unpaid Principal balance	2,000,000						2,000,000				3,000,000
Impaired loans with an allowance, related allowance	1,000,000	[3]					1,000,000	[3]			3,000,000	[3]
Foreign
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance, average recorded investment	2,000,000		6,000,000		9,000,000		4,000,000		9,000,000
Impaired loans with an allowance, interest income recognized	0		0		0		0		0
Impaired loans with an allowance, recorded investment	0						0				6,000,000
Impaired loans with an allowance, unpaid Principal balance	0						0				17,000,000
Impaired loans with an allowance, related allowance	$ 0	[3]					$ 0	[3]			$ 1,000,000	[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 less than $1 million of impaired loans in amounts individually less than $1 million at both Sept. 30, 2014 and Dec. 31, 2013. The allowance for loan loss associated with these loans totaled less than $1 million at both Sept. 30, 2014 and Dec. 31, 2013.

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