Retirement Benefits - Amounts Recognized in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Retirement Benefits [Abstract]
Balance at beginning of year	$ (2.2)	$ 0.0
Converted on October 1, 2016	0.0	(6.2)
Net actuarial loss amortized during the year	0.1	0.4
Net actuarial (loss) gain during the year	(1.4)	3.7
Non-controlling interest	0.1	(0.1)
Balance at end of year	$ (3.4)	$ (2.2)