Revenue Recognition - Dual Reporting - Consolidated Statement of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 261.4	$ 198.6	$ 687.7	$ 189.6
Currency translation adjustments	(2.7)	$ (95.7)	(12.2)	$ (35.3)
Impact of Adoption | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	1.9		(0.5)
Currency translation adjustments	0.0		0.2
Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	263.3		687.2
Currency translation adjustments	$ (2.7)		$ (12.0)