Securities financing activities - Schedule of securities purchased under resale agreements & securities borrowed collateral netting (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Securities purchased under resale agreements with an appropriate legal opinion:
Net asset balance	$ 214,644	$ 204,423
Amounts not nettable on the Consolidated Balance Sheets, Financial instruments	(211,255)	(201,375)
Amounts not nettable on the Consolidated Balance Sheets, Cash collateral	(518)	(246)
Net exposure	2,871	2,802
Securities borrowed:
Net asset balance	84,157	82,748
Amounts not nettable on the Consolidated Balance Sheets, Financial instruments	(81,413)	(80,338)
Amounts not nettable on the Consolidated Balance Sheets, Cash collateral	0	0
Net exposure	$ 2,744	$ 2,410