Segment And Geographic Information (Segment Table) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total net revenues	$ 1,396	$ 1,189	$ 1,043
Income before income taxes	761	458	506
Assets	54,673	48,734
Electronic Brokerage [Member]
Segment Reporting Information [Line Items]
Total net revenues	1,239	1,097	952
Income before income taxes	756	536	589
Assets	50,072	44,421	38,280
Market Making [Member]
Segment Reporting Information [Line Items]
Total net revenues	190	298	284
Income before income taxes	44	130	114
Assets	11,765	10,825	12,172
Corporate And Eliminations [Member]
Segment Reporting Information [Line Items]
Total net revenues	(33)	(206)	(193)
Income before income taxes	(39)	(208)	(197)
Assets	$ (7,164)	$ (6,512)	$ (7,067)

This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=51673353&loc=d3e41242-110953

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 10
-Article 5

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