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Debt - Long-term Debt (Details)								12 Months Ended
Debt - Long-term Debt (Details)	Aug. 12, 2020 USD ($)	Jul. 14, 2020 USD ($)	Jun. 30, 2020 USD ($)	Oct. 12, 2018 USD ($)	Oct. 12, 2018 EUR (€)	Oct. 09, 2018 USD ($)	Oct. 09, 2018 EUR (€)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2020 EUR (€)	Aug. 01, 2020 USD ($)	Jun. 30, 2020 EUR (€)	Jun. 29, 2020 USD ($)	Jun. 29, 2020 EUR (€)	Jun. 16, 2020	Sep. 30, 2019 EUR (€)	Apr. 30, 2019 EUR (€)	Oct. 09, 2018 EUR (€)	Mar. 14, 2018 USD ($)
Debt Instrument [Line Items]
Total long-term debt, including the current portion								$ 3,104,000,000	$ 2,974,000,000
Redemptions of senior notes								0	0	$ 635,000,000
Gain (loss) on extinguishment of debt								$ (34,000,000)	$ (7,000,000)	$ (31,000,000)
4.125% Senior Secured Notes due 2024
Debt Instrument [Line Items]
Interest rate								4.125%	4.125%	4.125%	4.125%						4.125%
4.875% Senior Secured Notes due 2024
Debt Instrument [Line Items]
Interest rate								4.875%	4.875%	4.875%	4.875%						4.875%
3.625% Senior Secured Notes
Debt Instrument [Line Items]
Interest rate								3.625%	3.625%	3.625%	3.625%						3.625%
5.500% Senior Notes due 2026
Debt Instrument [Line Items]
Interest rate								5.50%	5.50%	5.50%	5.50%						5.50%
Acquisition Corp.
Debt Instrument [Line Items]
Face or principal amount of debt instrument								$ 3,127,000,000	$ 2,998,000,000
Unamortized discount								1,000,000	3,000,000
Unamortized deferred financing costs								29,000,000	29,000,000
Issuance premium								7,000,000	8,000,000
Acquisition Corp. \| Senior Term Loan Facility due 2023
Debt Instrument [Line Items]
Total long-term debt, including the current portion								814,000,000	1,313,000,000
Face or principal amount of debt instrument								820,000,000	1,326,000,000
Redemptions of senior notes	$ 506,000,000
Unamortized discount								1,000,000	3,000,000
Unamortized deferred financing costs								5,000,000	10,000,000
Acquisition Corp. \| 5.000% Senior Secured Notes due 2023
Debt Instrument [Line Items]
Total long-term debt, including the current portion								$ 0	298,000,000
Face or principal amount of debt instrument		$ 244,000,000	$ 244,000,000											$ 244,000,000
Redemptions of senior notes		$ 295,000,000
Interest rate		5.00%	5.00%					5.00%			5.00%		5.00%	5.00%	5.00%	5.00%
Unamortized deferred financing costs												$ 6,000,000
Gain (loss) on extinguishment of debt		$ (6,000,000)
Acquisition Corp. \| 4.125% Senior Secured Notes due 2024
Debt Instrument [Line Items]
Total long-term debt, including the current portion								$ 0	336,000,000
Face or principal amount of debt instrument \| €													€ 311,000,000		€ 311,000,000
Redemptions of senior notes \| €					€ 34,500,000		€ 34,500,000
Interest rate			4.125%	4.125%	4.125%	4.125%		4.125%			4.125%		4.125%	4.125%	4.125%				4.125%
Gain (loss) on extinguishment of debt			$ (14,000,000)	$ (2,000,000)
Acquisition Corp. \| 4.875% Senior Secured Notes due 2024
Debt Instrument [Line Items]
Total long-term debt, including the current portion								$ 0	218,000,000
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%		4.875%	4.875%	4.875%				4.875%
Gain (loss) on extinguishment of debt			$ (10,000,000)			$ (1,000,000)		$ (24,000,000)
Acquisition Corp. \| 3.625% Senior Secured Notes
Debt Instrument [Line Items]
Total long-term debt, including the current portion								521,000,000	488,000,000
Face or principal amount of debt instrument								$ 519,000,000	487,000,000		€ 445,000,000						€ 445,000,000	€ 195,000,000	€ 250,000,000
Interest rate				3.625%	3.625%	3.625%		3.625%			3.625%							3.625%	3.625%
Unamortized deferred financing costs								$ 5,000,000	7,000,000
Issuance premium								7,000,000	8,000,000
Acquisition Corp. \| 2.750% Senior Secured Notes due 2028
Debt Instrument [Line Items]
Total long-term debt, including the current portion								375,000,000	0
Face or principal amount of debt instrument								$ 379,000,000			€ 325,000,000				€ 325,000,000
Interest rate			2.75%					2.75%			2.75%		2.75%	2.75%	2.75%
Unamortized deferred financing costs								$ 4,000,000
Acquisition Corp. \| 3.875% Senior Secured Notes due 2030
Debt Instrument [Line Items]
Total long-term debt, including the current portion								529,000,000	0
Face or principal amount of debt instrument								$ 535,000,000						$ 535,000,000
Interest rate			3.875%					3.875%			3.875%		3.875%	3.875%	3.875%
Unamortized deferred financing costs								$ 6,000,000
Acquisition Corp. \| 3.000% Senior Secured Notes due 2031
Debt Instrument [Line Items]
Total long-term debt, including the current portion								544,000,000	$ 0
Face or principal amount of debt instrument	$ 550,000,000							$ 550,000,000
Interest rate	3.00%							3.00%	3.00%		3.00%						3.00%
Unamortized deferred financing costs	$ 4,000,000							$ 6,000,000
Acquisition Corp. \| 5.500% Senior Notes due 2026
Debt Instrument [Line Items]
Total long-term debt, including the current portion								321,000,000	$ 321,000,000
Face or principal amount of debt instrument								$ 325,000,000												$ 325,000,000
Interest rate								5.50%			5.50%									5.50%
Unamortized deferred financing costs								$ 4,000,000
Acquisition Corp. \| Revolving Credit Facility
Debt Instrument [Line Items]
Total long-term debt, including the current portion								0	0
Line of credit facility, current borrowing capacity								300,000,000						$ 300,000,000
Letters of credit outstanding								10,000,000	13,000,000
Revolving credit facility outstanding								$ 0	$ 0