Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell Netting of financial instruments - repurchase agreements (Details) - Assets Sold under Agreements to Repurchase, Maturity Period [Domain] - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Assets Sold under Agreements to Repurchase [Line Items]
Carrying Value of Securities Purchased under Agreements to Resell and Deposits Paid for Securities Borrowed		$ 1,258	$ 1,122
Securities Purchased under Agreements to Resell, Amount Offset Against Collateral		0	0
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure	[1]	1,258	1,122
Held Financial Instruments, Not Separately Reported, Securities for Reverse Repurchase Agreements		1,246	1,112
Securities Borrowed or Purchased Under Agreements to Resell, Amount Not Offset Against Collateral		12	10
Securities Sold under Agreements to Repurchase, Gross		1,858	2,276
Securities Sold Under Agreements to Repurchase, Amount Offset Against Collateral		0	0
Securities Sold under Agreements to Repurchase		1,858	2,276
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements		1,858	2,276
Securities Sold Under Agreements to Repurchase, Amount Not Offset Against Collateral		$ 0	$ 0

[1] Excludes $92 million and $38 million of Fed funds sold, which are not subject to a master netting agreement at June 30, 2015 and December 31, 2014, respectively.