Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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

Commitments, Contingencies and Guarantees - Employee Retention Plan and Litigation (Details) - Unfavorable regulatory action $ in Millions	1 Months Ended
	May 31, 2017 EUR (€)	May 31, 2017 USD ($)	Jul. 31, 2016 EUR (€)	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)
Litigation
Amount of fine	€ 3,000,000	$ 3.5		€ 5,000,000	$ 5.4
Accrual for estimated loss	3,300,000	$ 3.9		€ 5,000,000	$ 5.4
Incremental charge	€ 300,000
Subsidiary of KCG
Litigation
Amount of fine			€ 400,000