Assets and Liabilities, at Fair Value - Available for Sale Securities in OCI (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Jun. 30, 2013	Jun. 30, 2014	Sep. 30, 2013
Assets and Liabilities, at Fair Value [Abstract]
Equity Investments in Exchange Stock - Cost		$ 3.7	$ 3.7
Equity Investments in Exchange Stock - Fair Value		4.3	4.4
Proceeds from Sale of Available-for-sale Securities	8.6
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax - LME Shares	6.3
Deferred Tax Liabilities, Accumulated Other Comprehensive Income - LME Shares	2.0
Proceeds from Shares of Exchanges Sold	1.5
Gain (Loss) on Sale of Exchange Shares	0.9
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		0.5	0.5
Deferred Income Taxes, Accumulated Other Comprehensive Income - AFS		$ (0.3)	$ (0.3)