Variable Interest Entities and Consolidated Sponsored Investment Products - Schedule of investments for which fair value was estimated using NAV (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments in funds products for which fair value was estimated using NAV	$ 695.8	$ 442.0
Global Fixed-Income Funds [Member] | Level 2 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments in funds products for which fair value was estimated using NAV	275.1	191.8
Hedge Funds [Member] | Level 2 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments in funds products for which fair value was estimated using NAV	27.2	6.6
Hedge Funds [Member] | Level 3 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments in funds products for which fair value was estimated using NAV	1.2	1.5
Real Estate and Private Equity Funds [Member] | Level 3 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments in funds products for which fair value was estimated using NAV	$ 392.3	$ 242.1