Other Income (Expenses) - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Income and Expenses [Abstract]
Proceeds from the sale of available-for-sale securities	$ 2.5	$ 27.7	$ 28.3	$ 253.7
Net gains recognized on trading investment securities	1.3	26.8	3.8	37.0
Net gains recognized on trading investment securities of consolidated SIPs	$ 19.9	$ 2.5	$ 25.8	$ 4.7