Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Obligations to Purchase Financial Instruments at a Future Date (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013
Financial Instruments Sold, Not yet Purchased, at Fair Value	$ 272.5	$ 179.9
Financial instrument sold, not yet purchased [Member]
Derivative, Fair Value, Net	$ 57.5	$ 30.7