Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Treasury Stock [Member]
Balance at Sep. 30, 2021	$ 1,342.7	$ 1.1	$ 1,489.1	$ (141.6)	$ (1.5)	$ (4.4)
Balance, Shares at Sep. 30, 2021		105.2
Net income (loss)	(1.3)			(1.3)
Other comprehensive income, net of tax	4.1				4.1
Capital contributions and issuance of common stock	1.6		1.6
Capital contributions and issuance of common stock, Shares		0.5
Equity-based compensation	14.0		14.0
Repurchase of common stock and distributions	(163.7)					163.7
Balance at Jun. 30, 2022	1,197.4	$ 1.1	1,504.7	(142.9)	2.6	(168.1)
Balance, Shares at Jun. 30, 2022		105.7
Balance at Mar. 31, 2022	1,253.5	$ 1.1	1,499.9	(153.7)	1.4	(95.2)
Balance, Shares at Mar. 31, 2022		105.7
Net income (loss)	10.8			10.8
Other comprehensive income, net of tax	1.2				1.2
Equity-based compensation	4.8		4.8
Repurchase of common stock and distributions	(72.9)					72.9
Balance at Jun. 30, 2022	1,197.4	$ 1.1	1,504.7	(142.9)	2.6	(168.1)
Balance, Shares at Jun. 30, 2022		105.7
Balance at Sep. 30, 2022	1,216.8	$ 1.1	1,509.5	(127.6)	2.0	(168.2)
Balance, Shares at Sep. 30, 2022		105.7
Net income (loss)	(24.1)			(24.1)
Other comprehensive income, net of tax	11.8				11.8
Capital contributions and issuance of common stock	1.5		1.5
Capital contributions and issuance of common stock, Shares		0.6
Equity-based compensation	15.7		15.7
Repurchase of common stock and distributions	(1.3)					1.3
Balance at Jun. 30, 2023	1,220.4	$ 1.1	1,526.7	(151.7)	13.8	(169.5)
Balance, Shares at Jun. 30, 2023		106.3
Balance at Mar. 31, 2023	1,185.9	$ 1.1	1,522.8	(168.5)	(0.1)	(169.4)
Balance, Shares at Mar. 31, 2023		106.4
Net income (loss)	16.8			16.8
Other comprehensive income, net of tax	13.9				13.9
Capital contributions and issuance of common stock, Shares		(0.1)
Equity-based compensation	3.9		3.9
Repurchase of common stock and distributions	(0.1)					0.1
Balance at Jun. 30, 2023	$ 1,220.4	$ 1.1	$ 1,526.7	$ (151.7)	$ 13.8	$ (169.5)
Balance, Shares at Jun. 30, 2023		106.3