Variable Interest Entities and Consolidated Sponsored Investment Products - Schedule of debt of consolidated VIEs and consolidated SIPs (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013
Variable Interest Entity [Line Items]
Debt of consolidated variable interest entities	$ 936.6	$ 988.5
Debt of consolidated sponsored investment products	122.8	108.9
Consolidated sponsored investment products [Member]
Variable Interest Entity [Line Items]
Effective Interest Rate	3.83%	4.08%
Total VIEs and SIPs [Member]
Variable Interest Entity [Line Items]
Debt of consolidated variable interest entities	936.6	988.5
Debt of consolidated sponsored investment products	122.8	108.9
Total Debt	$ 1,059.4	$ 1,097.4
Debt of Consolidated Variable Interest Entities At Fair Value [Member]
Variable Interest Entity [Line Items]
Effective Interest Rate	1.34%	1.32%