Earnings per Share (Schedule of Weighted-Average Shares Outstanding) (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Schedule Of Weighted Average Number Of Shares [Line Items]
Basic weighted-average shares outstanding (in shares)	51.4	53.6	51.5	54.0
Effect of dilutive securities (in shares)	0.6	0.7	0.5	0.6
Diluted weighted-average shares outstanding (in shares)		54.3	52.0	54.6
RSE and PRSE awards
Schedule Of Weighted Average Number Of Shares [Line Items]
Effect of dilutive securities (in shares)	0.6	0.7	0.5	0.6
Share options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive awards excluded from the calculation of diluted weighted-average shares outstanding (in shares)		1.2	0.8
RSE and PRSE awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive awards excluded from the calculation of diluted weighted-average shares outstanding (in shares)				0.1