Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Allowance for possible losses and sales returns - accounts receivable [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	$ 21.8	$ 25.1	$ 26.8
CHARGED TO COSTS AND EXPENSES	(5.0)	(2.5)	(4.3)
CHARGED TO OTHER ACCOUNTS	0.7	0.2	2.0
DEDUCTIONS NET OF RECOVERIES	(6.9)	(6.0)	(8.0)
BALANCE AS OF END OF PERIOD	20.6	21.8	25.1
Valuation allowance against deferred tax assets [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	80.2	58.2	26.9
CHARGED TO COSTS AND EXPENSES	(2.2)	(23.1)	30.8
CHARGED TO OTHER ACCOUNTS	4.5	0.0	0.0
DEDUCTIONS NET OF RECOVERIES	(41.9)	(1.1)	0.5
BALANCE AS OF END OF PERIOD	$ 45.0	$ 80.2	$ 58.2