Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell Netting of financial instruments - repurchase agreements (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Carrying Value of Securities Purchased under Agreements to Resell and Deposits Paid for Securities Borrowed		$ 1,274	$ 1,249
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure	[1]	1,274	1,249
Fair Value of Securities Received as Collateral that Can be Resold or Repledged		1,262	1,241
Securities Purchased under Agreements to Resell, Not Subject to Master Netting Arrangement		12	8
Securities Borrowed or Purchased Under Agreements to Resell, Amount Not Offset Against Collateral		0	0
Securities Sold under Agreements to Repurchase, Gross		1,704	1,633
Securities Sold under Agreements to Repurchase		1,704	1,633
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities		1,704	1,633
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 $18 million and $58 million of Fed funds sold, which are not subject to a master netting agreement at March 31, 2017 and December 31, 2016, respectively.