Goodwill - Goodwill by Segment (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Goodwill [Line Items]
Goodwill	$ 47.5	$ 47.5
Commodity and Risk Management [Member]
Goodwill [Line Items]
Goodwill	30.7	30.7
Foreign Exchange [Member]
Goodwill [Line Items]
Goodwill	6.3	6.3
Other Segment [Member]
Goodwill [Line Items]
Goodwill	2.4	2.4
Securities Segment [Member]
Goodwill [Line Items]
Goodwill	8.1	8.1
Scenario, Previously Reported [Member] | Commodity and Risk Management [Member]
Goodwill [Line Items]
Goodwill		$ 33.1