Retirement Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Retirement Benefits [Abstract]
Defined contribution plan expense	$ 3.7	$ 2.9	$ 8.4	$ 6.6