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	Sep. 30, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 57,527	[1]	$ 51,657	[1]
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,558		1,647
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,403		2,010
Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	14,574		14,359
Wealth management mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans	5,359		4,834
Wealth management loans and mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans	10,825		9,818
Investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,326		1,323
Investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,603		1,444
Investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	12,837		12,598
Investment grade | Wealth management loans:
Financing Receivable, Recorded Investment [Line Items]
Loans	5,396		4,920
Non-investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	232		324
Non-investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	800		566
Non-investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	1,737		1,761
Non-investment grade | Wealth management loans:
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 70		$ 64

[1] Net of unearned income of $894 million at Sept. 30, 2014 and $1,020 million at Dec. 31, 2013 primarily on domestic and foreign lease financings.