Loans and asset quality - Credit Quality Indicators - Wealth Management Loans and Mortgages - Credit Risk Profile by Internally Assigned Grade (Detail) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	$ 61,661	$ 63,703
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans		2,331	2,342
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans		4,326	3,945
Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans		12,903	15,899
Wealth management mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans		6,989	6,647
Wealth management loans and mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans		13,975	13,347
Investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans		2,014	2,026
Investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans		3,276	2,678
Investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans		9,527	13,965
Investment grade | Wealth management loans
Financing Receivable, Recorded Investment [Line Items]
Loans		6,813	6,529
Non-investment grade | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans		317	316
Non-investment grade | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans		1,050	1,267
Non-investment grade | Financial institutions
Financing Receivable, Recorded Investment [Line Items]
Loans		3,376	1,934
Non-investment grade | Wealth management loans
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 173	$ 171

[1] Net of unearned income of $592 million at March 31, 2016 and $674 million at Dec. 31, 2015 primarily on domestic and foreign lease financings.