Securities financing activities - Schedule of securities purchased under resale agreements, netting & securities borrowed (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Securities purchased under resale agreements:
Securities purchased under resale agreements with an appropriate legal opinion, Gross asset balance	$ 375,841	$ 347,142
Amounts netted on the Consolidated balance sheets	(161,197)	(142,719)
Securities purchased under resale agreements with an appropriate legal opinion, Net asset balance	214,644	204,423
Securities purchased under resale agreements where an appropriate legal opinion has not been either sought or obtained, Gross asset balance	2,710	10,598
Total securities purchased under resale agreements, gross asset balance	378,551	357,740
Total securities purchased under resale agreements, net asset balance	217,354	215,021
Securities borrowed, Gross asset balance	105,668	110,435
Securities borrowed where an appropriate legal opinion has not been either sought or obtained	21,500	27,700
Securities Financing Transaction, Fair Value
Securities purchased under resale agreements:
Total securities purchased under resale agreements, net asset balance	27,400	28,600
Securities borrowed, fair value	$ 405	$ 992