Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share, Diluted, by Common Class, Including Two Class Method
Net earnings available to common stockholders for basic earnings per share	$ 30.9	$ 1.3	$ 75.1	$ 9.5
Dilutive impact of net earnings attributable to NCI	0.0	0.0	0.0	0.0
Net earnings available to common stockholders for diluted earnings per share	$ 30.9	$ 1.3	$ 75.1	$ 9.5
Weighted Average shares of Common Stock Outstanding, basic (in shares)	133.4	62.7	134.1	51.0
Weighted-Average shares of Common Stock Outstanding, diluted (in shares)	134.5	62.9	134.8	51.2
Earnings per share of Common Stock, basic (in USD per share)	$ 0.23	$ 0.02	$ 0.56	$ 0.19
Earnings per share of Common Stock, diluted (in USD per share)	$ 0.23	$ 0.02	$ 0.56	$ 0.19
BRBR Stock Option
Earnings Per Share, Diluted, by Common Class, Including Two Class Method
Dilutive restricted stock units, (in shares)	0.1	0.0	0.1	0.0
Restricted Stock Units (RSUs)
Earnings Per Share, Diluted, by Common Class, Including Two Class Method
Dilutive restricted stock units, (in shares)	0.2	0.2	0.2	0.2
Antidilutive securities excluded from computation of earnings per share, amount	0.0	0.2	0.1	0.1
Performance-Based Restricted Stock Units
Earnings Per Share, Diluted, by Common Class, Including Two Class Method
Dilutive restricted stock units, (in shares)	0.8	0.0	0.4	0.0
Antidilutive securities excluded from computation of earnings per share, amount	0.0	0.1	0.3	0.1