Debt - Long-term Debt Footnote (Detail)				3 Months Ended			9 Months Ended
		Nov. 05, 2018 USD ($)	Oct. 12, 2018 USD ($)	Jun. 30, 2019 USD ($)		Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)		Jun. 30, 2018 USD ($)	Jun. 30, 2019 EUR (€)	May 16, 2019 USD ($)	Apr. 30, 2019	Oct. 09, 2018 USD ($)	Sep. 30, 2018 USD ($)		Sep. 30, 2018 EUR (€)	Mar. 14, 2018 USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of debt				$ 4,000,000		$ 7,000,000	$ 7,000,000		$ 31,000,000
Acquisition Corp.
Debt Instrument [Line Items]
Face or principal amount of debt instrument				3,030,000,000			3,030,000,000							$ 2,851,000,000
Unamortized discount				3,000,000			3,000,000							4,000,000
Unamortized deferred financing costs				29,000,000			29,000,000							28,000,000
Unamortized premium														0
Debt outstanding	[1]			3,006,000,000			3,006,000,000							2,819,000,000
Acquisition Corp. | Revolving Credit Facility
Debt Instrument [Line Items]
Commitments under revolving credit facility				180,000,000			180,000,000							180,000,000
Letters of credit outstanding				13,000,000			13,000,000							8,000,000
Revolving credit facility outstanding				0			0							0
Debt outstanding	[2]			0			0							0
Senior Term Loan Facility due 2023 | Acquisition Corp.
Debt Instrument [Line Items]
Face or principal amount of debt instrument				1,326,000,000			1,326,000,000
Unamortized discount				3,000,000			3,000,000
Unamortized deferred financing costs				10,000,000			10,000,000							12,000,000
Debt outstanding	[3]			$ 1,313,000,000			$ 1,313,000,000							1,310,000,000
5.625% Senior Secured Notes due 2022
Debt Instrument [Line Items]
Interest rate				5.625%		5.625%	5.625%		5.625%	5.625%
5.625% Senior Secured Notes due 2022 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate		5.625%		5.625%			5.625%			5.625%		5.625%	5.625%
Loss on extinguishment of debt		$ 1,000,000					$ 4,000,000
Debt outstanding				$ 0	[4]		$ 0	[4]			$ 221,000,000			246,000,000	[4]
5.000% Senior Secured Notes due 2023 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate				5.00%			5.00%			5.00%
Face or principal amount of debt instrument				$ 300,000,000			$ 300,000,000
Unamortized deferred financing costs				2,000,000			2,000,000							2,000,000
Debt outstanding	[5]			$ 298,000,000			$ 298,000,000							297,000,000
4.125% Senior Secured Notes due 2024 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate			4.125%	4.125%			4.125%			4.125%			4.125%
Loss on extinguishment of debt			$ 2,000,000
Face or principal amount of debt instrument				$ 353,000,000			$ 353,000,000			€ 310,500,000				402,000,000		€ 345,000,000
Unamortized deferred financing costs				4,000,000			4,000,000							3,000,000
Debt outstanding	[6]			$ 349,000,000			$ 349,000,000							399,000,000
4.875% Senior Secured Notes due 2024
Debt Instrument [Line Items]
Interest rate				4.875%		4.875%	4.875%		4.875%	4.875%
4.875% Senior Secured Notes due 2024 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate				4.875%			4.875%			4.875%			4.875%
Face or principal amount of debt instrument				$ 220,000,000			$ 220,000,000						$ 30,000,000	250,000,000
Unamortized deferred financing costs				2,000,000			2,000,000							3,000,000
Debt outstanding	[7]			$ 218,000,000			$ 218,000,000							247,000,000
3.625% Senior Secured Notes due 2026 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate				3.625%			3.625%			3.625%
Face or principal amount of debt instrument				$ 506,000,000			$ 506,000,000			€ 445,000,000
Unamortized deferred financing costs				7,000,000			7,000,000
Unamortized premium				8,000,000			8,000,000
Debt outstanding	[8]			$ 507,000,000			$ 507,000,000							0
5.500% Senior Notes due 2026 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate				5.50%			5.50%			5.50%							5.50%
Face or principal amount of debt instrument				$ 325,000,000			$ 325,000,000							325,000,000			$ 325,000,000
Unamortized deferred financing costs				4,000,000			4,000,000							5,000,000
Debt outstanding	[9]			$ 321,000,000			$ 321,000,000							$ 320,000,000

[1] Principal amount of debt of $3.030 billion and $2.851 billion, an additional issuance premium of $8 million and nil, less unamortized discount of $3 million and $4 million and unamortized deferred financing costs of $29 million and $28 million at June 30, 2019 and September 30, 2018, respectively.

[2] Reflects $180 million of commitments under the Revolving Credit Facility available at both June 30, 2019 and September 30, 2018, less letters of credit outstanding of approximately $13 million at June 30, 2019 and $8 million at September 30, 2018. There were no loans outstanding under the Revolving Credit Facility at June 30, 2019 or September 30, 2018.

[3] Principal amount of $1.326 billion less unamortized discount of $3 million and unamortized deferred financing costs of $10 million and $12 million at June 30, 2019 and September 30, 2018, respectively.

[4] On May 16, 2019, Acquisition Corp. redeemed the remaining $221 million of its outstanding 5.625% Senior Notes due 2022. The Company recorded a loss on extinguishment of debt of approximately $4 million as a result of the debt redemption, which represents the premium paid on early redemption and unamortized deferred financing costs.

[5] Principal amount of $300 million less unamortized deferred financing costs of $2 million at both June 30, 2019 and September 30, 2018.

[6] Face amount of €311 million and €345 million at June 30, 2019 and September 30, 2018 respectively. Above amounts represent the dollar equivalent of such note at June 30, 2019 and September 30, 2018. Principal amount of $353 million and $402 million at June 30, 2019 and September 30, 2018, respectively, less unamortized deferred financing costs of $4 million and $3 million at June 30, 2019 and September 30, 2018, respectively.

[7] Principal amount of $220 million and $250 million less unamortized deferred financing costs of $2 million and $3 million at June 30, 2019 and September 30, 2018, respectively.

[8] Face amount of €445 million at June 30, 2019. Above amounts represent the dollar equivalent of such note at June 30, 2019. Principal amount of $506 million, an additional issuance premium of $8 million, less unamortized deferred financing costs of $7 million at June 30, 2019.

[9] Principal amount of $325 million and $325 million less unamortized deferred financing costs of $4 million and $5 million at June 30, 2019 and September 30, 2018, respectively.