Number of different types of foreign currencies the company trades

No definition available.

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- Definition

Number of commercial and institutional clients

+ References

No definition available.

+ Details

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- Definition

Number retail clients

+ References

No definition available.

+ Details

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- Definition

Amount of capitalized cost for obtaining membership with right to do business on trading exchange.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 340
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99387790&loc=d3e43427-110978

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- Definition

The number of countries in which the entity operates as of balance sheet date.

+ References

No definition available.

+ Details

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- Definition

The amount of a reclassification adjustment made to prior period financial statement amounts.

+ References

No definition available.

+ Details

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Description of Business and Significant Accounting Policies - Accounts, Customers and Other Facts (Details) $ in Millions	12 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Number of different types of foreign currencies	140
Number of commercial and institutional clients	20,000
Number retail clients	80,000
Number of Countries in which Entity Operates	130
Non-Trading Technology and Support [Member]
Prior Period Reclassification Adjustment			$ 11.6
communications [Member]
Prior Period Reclassification Adjustment			5.0
Commission and Clearing Fees
Prior Period Reclassification Adjustment		$ 35.0	$ 35.2
Exchange memberships not representing an ownership interest [Member]
Memberships in Exchanges Owned	$ 5.8
Exchange memberships representing an ownership interest [Member]
Memberships in Exchanges Owned	$ 5.6