Consolidated Statements of Changes in Stockholders' Equity (Deficit) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning Balance (in shares) at Sep. 30, 2018		110,200,000
Beginning Balance at Sep. 30, 2018	$ 2,051	$ 1	$ 1,745	$ 287	$ 18
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of shares redeemed and canceled, under employee stock option plan (in shares)		800,000
Issuance of common stock, net of shares redeemed and canceled, under employee stock option plan	0
Stock Repurchased During Period, Shares		(300,000)
Amortization of share-based compensation	6		6
Net income (loss)	9
Other comprehensive income (loss)	(20)				(20)
Shares repurchased and retired for tax withholding on vesting of restricted stock units	(6)		(6)
Ending Balance at Dec. 31, 2018	2,132	$ 1	1,745	388	(2)
Ending Balance (in shares) at Dec. 31, 2018		110,700,000
Beginning Balance (in shares) at Sep. 30, 2018		110,200,000
Beginning Balance at Sep. 30, 2018	2,051	$ 1	1,745	287	18
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(4)
Other comprehensive income (loss)	(12)
Ending Balance at Mar. 31, 2019	2,135	$ 1	1,750	378	6
Ending Balance (in shares) at Mar. 31, 2019		110,700,000
Beginning Balance (in shares) at Dec. 31, 2018		110,700,000
Beginning Balance at Dec. 31, 2018	2,132	$ 1	1,745	388	(2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of share-based compensation	5
Net income (loss)	(13)
Other comprehensive income (loss)	8
Ending Balance at Mar. 31, 2019	2,135	$ 1	1,750	378	6
Ending Balance (in shares) at Mar. 31, 2019		110,700,000
Beginning Balance (in shares) at Sep. 30, 2019		111,000,000.0
Beginning Balance at Sep. 30, 2019	1,300	$ 1	$ 1,761	(289)	(173)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of shares redeemed and canceled, under employee stock option plan (in shares)		300,000
Issuance of common stock, net of shares redeemed and canceled, under employee stock option plan	$ 0
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		100,000
Stock Repurchased and Retired During Period, Shares	(142,000,000)	(10,700,000)	(142,000,000)
Amortization of share-based compensation	$ 6		$ 6
Preferred Stock, Accretion of Redemption Discount	(4)		(4)
Accrued dividends on Series A preferred stock	(1)		(1)
Net income (loss)	(54)
Other comprehensive income (loss)	10				10
Shares repurchased and retired for tax withholding on vesting of restricted stock units	(2)		(2)
Ending Balance at Dec. 31, 2019	1,113	$ 1	1,618	(343)	(163)
Ending Balance (in shares) at Dec. 31, 2019		100,500,000
Beginning Balance (in shares) at Sep. 30, 2019		111,000,000.0
Beginning Balance at Sep. 30, 2019	$ 1,300	$ 1	1,761	(289)	(173)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Repurchased During Period, Shares	(28,923,664)
Accrued dividends on Series A preferred stock	$ (2)
Net income (loss)	(726)
Other comprehensive income (loss)	(45)
Ending Balance at Mar. 31, 2020	204	$ 1	1,436	(1,015)	(218)
Ending Balance (in shares) at Mar. 31, 2020		82,700,000
Beginning Balance (in shares) at Dec. 31, 2019		100,500,000
Beginning Balance at Dec. 31, 2019	1,113	$ 1	$ 1,618	(343)	(163)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of shares redeemed and canceled, under employee stock option plan (in shares)		600,000
Issuance of common stock, net of shares redeemed and canceled, under employee stock option plan	$ 0
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		200,000
Stock Repurchased and Retired During Period, Shares	(188,000,000)	(18,200,000)	(188,000,000)
Stock Repurchased During Period, Shares	(18,206,273)
Amortization of share-based compensation	$ 8		$ 8
Accrued dividends on Series A preferred stock	(1)		(1)
Net income (loss)	(672)
Other comprehensive income (loss)	(55)
Shares repurchased and retired for tax withholding on vesting of restricted stock units	(1)		(1)
Ending Balance at Mar. 31, 2020	$ 204	$ 1	$ 1,436	$ (1,015)	$ (218)
Ending Balance (in shares) at Mar. 31, 2020		82,700,000