Revenue Recognition - Dual Reporting - Consolidated Statement of Shareowners' Equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Oct. 01, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings, beginning balance	$ 1,336.3	$ 1,947.2	$ 1,336.3	$ 1,947.2			$ 1,617.5
Net income (loss)	346.0	227.4	426.3	(9.0)
Other comprehensive income	36.6	94.2	1.6	97.7
Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income (loss)	341.2		423.8
Retained earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings, beginning balance	6,398.0	5,880.9	6,398.0	5,880.9	$ 6,167.6	$ 6,204.2	6,198.1	$ 5,759.7	$ 6,103.4
Net income (loss)	346.0	227.4	426.3	(9.0)
Retained earnings | Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings, beginning balance					6,163.8	6,198.1
Net income (loss)	341.2		423.8
Accumulated other comprehensive loss
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings, beginning balance	(940.3)	(1,081.5)	(940.3)	(1,081.5)	(976.9)		$ (941.9)	$ (1,175.7)	$ (1,179.2)
Other comprehensive income	36.6	$ 94.2	1.6	$ 97.7
Accumulated other comprehensive loss | Balances without adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other comprehensive income	36.6		1.8
Accounting Standards Update 2014-09 | Impact of Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income (loss)	(4.8)		(2.5)
Accounting Standards Update 2014-09 | Retained earnings | Impact of Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings, beginning balance					$ (3.8)	$ (6.1)
Net income (loss)	(4.8)		(2.5)
Accounting Standards Update 2014-09 | Accumulated other comprehensive loss | Impact of Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other comprehensive income	$ 0.0		$ 0.2