Investments - Summary of gross unrealized losses and fair values of investment securities in a continuous unrealized loss position (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 34.4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		(0.8)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		21.7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		(1.0)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		56.1
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(1.8)
Sponsored Investment Products [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	50.3	30.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(2.4)	(0.7)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1.4	21.7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(0.1)	(1.0)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	51.7	51.7
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(2.5)	(1.7)
Other equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		4.4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		(0.1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		4.4
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ (0.1)