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Revenue Recognition - Dual Reporting - Consolidated Statement of Cash Flows (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
Receivables			(34.4)	(37.7)
Contract liabilities			26.5	22.5
Income taxes			(66.3)	495.2
Other assets and liabilities			1.8	$ 9.9
Impact of Adoption \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	1.9		(0.5)
Receivables			(1.6)
Contract liabilities			1.5
Income taxes			(0.2)
Other assets and liabilities			0.8
Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 263.3		687.2
Receivables			(36.0)
Contract liabilities			28.0
Income taxes			(66.5)
Other assets and liabilities			$ 2.6