Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Other Current Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Current	$ 14.9	$ 20.3
Other Noncurrent Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Noncurrent	3.0	0.5
US Treasury and Government [Member] | Other Current Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Current	14.3	13.1
US Treasury and Government [Member] | Other Noncurrent Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Noncurrent	3.0	0.5
Corporate Debt Securities [Member] | Other Current Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Current	0.0	0.2
Corporate Debt Securities [Member] | Other Noncurrent Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Noncurrent	0.0	0.0
US States and Political Subdivisions Debt Securities [Member] | Other Current Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Current	0.6	7.0
US States and Political Subdivisions Debt Securities [Member] | Other Noncurrent Assets [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Noncurrent	$ 0.0	$ 0.0