Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell Netting of financial instruments - repurchase agreements (Details) - USD ($) $ in Millions		Dec. 31, 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		$ 1,239	$ 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]	1,239	1,122
Fair Value of Securities Received as Collateral that Can be Resold or Repledged		1,229	1,112
Securities Borrowed or Purchased Under Agreements to Resell, Amount Not Offset Against Collateral		10	10
Securities Sold under Agreements to Repurchase, Gross		1,654	2,276
Securities Sold Under Agreements to Repurchase, Amount Offset Against Collateral		0	0
Securities Sold under Agreements to Repurchase		1,654	2,276
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities		1,654	2,276
Securities Sold Under Agreements to Repurchase, Amount Not Offset Against Collateral		$ 0	$ 0

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