Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell Netting of financial instruments - repurchase agreements (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Assets Sold under Agreements to Repurchase [Line Items]
Carrying Value of Securities Purchased under Agreements to Resell and Deposits Paid for Securities Borrowed		$ 1,102	$ 1,239
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure	[1]	1,102	1,239
Fair Value of Securities Received as Collateral that Can be Resold or Repledged		1,092	1,229
Securities Purchased under Agreements to Resell, Not Subject to Master Netting Arrangement		10	10
Securities Borrowed or Purchased Under Agreements to Resell, Amount Not Offset Against Collateral		0	0
Securities Sold under Agreements to Repurchase, Gross		1,622	1,654
Securities Sold under Agreements to Repurchase		1,622	1,654
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities		1,622	1,654
Securities Sold under Agreements to Repurchase, Not Subject to Master Netting Arrangement		0	0
Securities Sold Under Agreements to Repurchase, Amount Not Offset Against Collateral		$ 0	$ 0

[1] Excludes $5 million and $38 million of Fed funds sold, which are not subject to a master netting agreement at June 30, 2016 and December 31, 2015, respectively