Consolidated Statements of Stockholders' Deficit - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common stock	Paid-in capital	Retained (deficit) earnings	Retained (deficit) earnings Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated other comprehensive income
Common stock outstanding, beginning balance (in shares) at Sep. 30, 2018			188
Balance at beginning of period at Sep. 30, 2018	$ (358)		$ 2	$ 7	$ (399)		$ 32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 208				208
Dividends paid per common share (usd per share)	$ 0.424
Dividends paid	$ (80)				(80)
Stock-based compensation, net of issuances	6			6
Common stock outstanding, ending balance (in shares) at Sep. 30, 2019			188
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(21)						(21)
Balance at end of period at Sep. 30, 2019	(258)	$ (13)	$ 2	13	(284)	$ (13)	11
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 317				317
Dividends paid per common share (usd per share)	$ 0.452
Dividends paid	$ (84)				(84)
Stock-based compensation, net of issuances	11			11
Repurchase of common stock (in shares)			(3)
Repurchase of common stock	$ (60)				(60)
Common stock outstanding, ending balance (in shares) at Sep. 30, 2020	185		185
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ (3)						(3)
Balance at end of period at Sep. 30, 2020	(76)	1	$ 2	24	(110)	$ 1	8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 420				420
Dividends paid per common share (usd per share)	$ 0.500
Dividends paid	$ (90)				(91)
Stock-based compensation, net of issuances	10			10
Repurchase of common stock (in shares)			(5)
Repurchase of common stock	$ (127)				(127)
Common stock outstanding, ending balance (in shares) at Sep. 30, 2021	180		180
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ 0
APIC, Share-based Payment Arrangement, Increase for Cost Recognition				1
Balance at end of period at Sep. 30, 2021	$ 135	$ (2)	$ 2	$ 35	$ 90		$ 8