Securities financing activities - Schedule of securities sold under repurchase agreements, netting & securities loaned (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Securities Financing Transaction [Line Items]
Securities sold under repurchase agreements with an appropriate legal opinion, Gross liability balance	$ 311,565,000,000	$ 290,529,000,000
Amounts netted on the Consolidated balance sheets	(161,197,000,000)	(142,719,000,000)
Securities sold under repurchase agreements with an appropriate legal opinion, Net liability balance	150,368,000,000	147,810,000,000
Securities sold under repurchase agreements where an appropriate legal opinion has not been either sought or obtained(a)	14,070,000,000	21,996,000,000
Total securities sold under repurchase agreements, Gross liability balance	325,635,000,000	312,525,000,000
Total securities sold under repurchase agreements, Net liability balance	164,438,000,000	169,806,000,000
Securities loaned	20,738,000,000	25,927,000,000
Securities loaned where an appropriate legal opinion has not been either sought or obtained	41,000,000	271,000,000
Securities-For-Securities Borrow Versus Pledge Transactions
Securities Financing Transaction [Line Items]
Securities lending transactions and fair value	5,800,000,000	4,100,000,000
Securities Financing Transaction, Fair Value
Securities Financing Transaction [Line Items]
Total securities sold under repurchase agreements, Net liability balance	3,600,000,000	3,000,000,000
Securities lending transactions and fair value	$ 0	$ 0