Condensed Consolidated Statements of Stockholders' Deficit - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
Common stock outstanding, at beginning of period (shares) at Sep. 30, 2019			188
Balance at beginning of period at Sep. 30, 2019	$ (258)	$ 1	$ 2	$ 13	$ (284)	$ 11
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	73				73
Dividends paid	(21)				(21)
Stock-based compensation, net of issuances	3			3
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	6					6
Common stock outstanding, at end of period (shares) at Dec. 31, 2019			188
Balance at end of period at Dec. 31, 2019	$ (196)		$ 2	16	(231)	17
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends paid per common share (usd per share)	$ 0.113
Common stock outstanding, at beginning of period (shares) at Sep. 30, 2019			188
Balance at beginning of period at Sep. 30, 2019	$ (258)	1	$ 2	13	(284)	11
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	136
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(17)
Common stock outstanding, at end of period (shares) at Mar. 31, 2020			185
Balance at end of period at Mar. 31, 2020	(237)		$ 2	16	(249)	(6)
Common stock outstanding, at beginning of period (shares) at Dec. 31, 2019			188
Balance at beginning of period at Dec. 31, 2019	(196)		$ 2	16	(231)	17
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	63				63
Dividends paid	(21)				(21)
Repurchases of common stock	(60)				(60)
Stock Repurchased and Retired During Period, Shares			3
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(23)					(23)
Common stock outstanding, at end of period (shares) at Mar. 31, 2020			185
Balance at end of period at Mar. 31, 2020	$ (237)		$ 2	16	(249)	(6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends paid per common share (usd per share)	$ 0.113
Common stock outstanding, at beginning of period (shares) at Sep. 30, 2020	185		185
Balance at beginning of period at Sep. 30, 2020	$ (76)	(2)	$ 2	24	(110)	8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	87				87
Dividends paid	(23)				(23)
Stock-based compensation, net of issuances	1			1
Repurchases of common stock	(58)
Stock Repurchased and Retired During Period, Shares			2
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	16					16
Common stock outstanding, at end of period (shares) at Dec. 31, 2020			183
Balance at end of period at Dec. 31, 2020	$ (55)		$ 2	25	(106)	24
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends paid per common share (usd per share)	$ 0.125
Common stock outstanding, at beginning of period (shares) at Sep. 30, 2020	185		185
Balance at beginning of period at Sep. 30, 2020	$ (76)	$ (2)	$ 2	24	(110)	8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	155
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ 8
Common stock outstanding, at end of period (shares) at Mar. 31, 2021	181		181
Balance at end of period at Mar. 31, 2021	$ (56)		$ 2	29	(103)	16
Common stock outstanding, at beginning of period (shares) at Dec. 31, 2020			183
Balance at beginning of period at Dec. 31, 2020	(55)		$ 2	25	(106)	24
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	68				68
Dividends paid	(23)				(23)
Stock-based compensation, net of issuances	4			4
Repurchases of common stock	(42)				(42)
Stock Repurchased and Retired During Period, Shares			2
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ (8)					(8)
Common stock outstanding, at end of period (shares) at Mar. 31, 2021	181		181
Balance at end of period at Mar. 31, 2021	$ (56)		$ 2	$ 29	$ (103)	$ 16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends paid per common share (usd per share)	$ 0.125