Securities Financing Activities - Transfers Not Qualifying for Sale Accounting (Details) - USD ($) $ in Billions	Sep. 30, 2018	Dec. 31, 2017
Securities Financing Transactions Disclosures [Abstract]
Transfers not qualifying for sale accounting	$ 1.6	$ 1.5

Carrying amount of financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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