Basis of Presentation (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Sep. 30, 2016	Sep. 30, 2015
Entity Information [Line Items]
Cash and cash equivalents, Carrying value	$ 1,268.7	$ 1,150.3	$ 1,303.2	$ 1,383.8
Subsidiaries [Member]
Entity Information [Line Items]
Cash and cash equivalents, Carrying value		$ 40.1	$ 40.5
Other Segments [Member]
Entity Information [Line Items]
General and administrative expense	1.6
Other income	$ 1.7