Assets and Liabilities, at Fair Value Assets and Liabilities, at Fair Value - Available for Sale Securities in OCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Sep. 30, 2012
Assets and Liabilities, at Fair Value [Abstract]
Gain (Loss) on Sale of Exchange Shares	$ 0.9
Equity Investments in Exchange Stock - Cost	4.0
Equity Investments in Exchange Stock - Fair Value	3.4	12.4
Proceeds from Sale of Available-for-sale Securities	8.6
Proceeds from Shares of Exchanges Sold	1.5
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
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax - Other Exchange Shares	0.4
Deferred Tax Assets, Accumulated Other Comprehensive Income - Other Exchange Shares	$ (0.2)