Deposits - Types and Sources of the Firm's Deposits (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Deposits at fair value	$ 22,902	$ 13,782
Weighted average maturity of time deposits	2 years	2 years 6 months
Deposits insured by the FDIC	$ 75,020	$ 69,910

Period of time between issuance and maturity of customer deposits, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration