Assets and Liabilities, at Fair Value - Available for Sale Securities in OCI (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Assets and Liabilities, at Fair Value [Abstract]
Equity Investments in Exchange Stock - Cost	$ 3.7	$ 3.9
Equity Investments in Exchange Stock - Fair Value	$ 10.2	$ 8.3