Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Securities Purchased under Agreements to Resell [Abstract]
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	$ 1,100	$ 1,100
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 219	$ 222

Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

Name:	us-gaap_FairValueOfSecuritiesReceivedAsCollateralThatHaveBeenResoldOrRepledged
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant