Revenue Recognition - Dual Reporting - Consolidated Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income (loss)	$ 80.3	$ (236.4)
Receivables	(6.1)	(18.4)
Contract liabilities	26.9	27.9
Income taxes	12.2	508.0
Other assets and liabilities	(4.3)	$ (0.3)
Impact of Adoption | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income (loss)	2.3
Receivables	(1.3)
Contract liabilities	(1.1)
Income taxes	0.6
Other assets and liabilities	(0.5)
Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income (loss)	82.6
Receivables	(7.4)
Contract liabilities	25.8
Income taxes	12.8
Other assets and liabilities	$ (4.8)