Loans and asset quality- Credit Quality Indicators - Wealth Management Loans and Mortgages - Credit Risk Profile by Internally Assigned Grade (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 54,036	$ 51,657
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,959	1,647
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,145	2,010
Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	13,576	14,359
Wealth management mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans	4,928	4,834
Wealth management loans and mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans	10,004	9,818
Investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,630	1,323
Investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,518	1,444
Investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	11,961	12,598
Investment grade | Wealth management loans:
Financing Receivable, Recorded Investment [Line Items]
Loans	5,009	4,920
Non-investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	329	324
Non-investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	627	566
Non-investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	1,615	1,761
Non-investment grade | Wealth management loans:
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 67	$ 64