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, 2015		Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 62,326	[1]	$ 59,132	[1]
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,971		1,642
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	3,062		2,530
Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	14,667		13,319
Wealth management mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans	5,713		5,534
Wealth management loans and mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans	11,649		11,184
Investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,711		1,381
Investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,082		1,641
Investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	12,753		11,576
Investment grade | Wealth management loans:
Financing Receivable, Recorded Investment [Line Items]
Loans	5,848		5,621
Non-investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	260		261
Non-investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	980		889
Non-investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	1,914		1,743
Non-investment grade | Wealth management loans:
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 88		$ 29

[1] Net of unearned income of $843 million at March 31, 2015 and $866 million at Dec. 31, 2014 primarily on domestic and foreign lease financings.