Assets and Liabilities, at Fair Value Level 4 - Available for Sale Securities - Fin Inst (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Sep. 30, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 796.4	$ 448.9
Available-for-sale Securities, Gross Unrealized Gains	0.1	0.3
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Debt Securities	797.0	454.7
Financial instruments owned [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	0.5	5.5
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Debt Securities	0.5	5.5
Available-for-sale Securities, Gross Unrealized Gain (Loss)	0.1	0.1
US Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	0.5	0.5
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Debt Securities	0.5	0.5
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		5.0
Available-for-sale Securities, Gross Unrealized Gains		0
Available-for-sale Securities, Gross Unrealized Losses		0
Available-for-sale Securities, Debt Securities		$ 5.0

Amount of debt securities categorized neither as held-to-maturity nor trading.

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details