Other Expenses Level 4 - Other Expenses Breakout (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 7.4	$ 6.1	$ 24.8	$ 20.6
Travel and Entertainment Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	2.3	2.4	8.6	6.3
Non-trading hardware and software maintenance and software licensing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.4	0.7	1.8	2.1
Contingent Consideration [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.5	0.3	2.7	3.8
Insurance Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.4	0.4	1.2	1.1
Taxes Other than Income and Excise Taxes [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	1.1	0.7	3.0	2.0
Advertising, Meetings and Conferences [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.7	0.4	1.8	1.4
Office supplies and printing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.3	0.3	1.0	0.8
Other Operating Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 1.7	$ 0.9	$ 4.7	$ 3.1