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Debt - Open Market Purchase (Details) - USD ($)			12 Months Ended
	Jun. 30, 2020	Oct. 09, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Jun. 29, 2020
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt			$ (34,000,000)	$ (7,000,000)	$ (31,000,000)
Acquisition Corp.
Debt Instrument [Line Items]
Face or principal amount of debt instrument			$ 3,127,000,000	$ 2,998,000,000
4.875% Senior Secured Notes
Debt Instrument [Line Items]
Interest rate			4.875%	4.875%	4.875%
4.875% Senior Secured Notes | Acquisition Corp.
Debt Instrument [Line Items]
Face or principal amount of debt instrument	$ 220,000,000	$ 30,000,000				$ 220,000,000
Interest rate	4.875%	4.875%	4.875%			4.875%
Debt instrument remaining outstanding amount	$ 230,000,000	$ 220,000,000
Gain (loss) on extinguishment of debt	$ (10,000,000)	$ (1,000,000)	$ (24,000,000)

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Debt instrument remaining outstanding amount.

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