Debt - Additional Information (Detail) € in Millions			3 Months Ended		6 Months Ended
	Apr. 15, 2021 USD ($)	Mar. 08, 2021 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Apr. 14, 2021 USD ($)	Mar. 31, 2021 EUR (€)	Jan. 20, 2021 USD ($)	Nov. 02, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 EUR (€)	Aug. 12, 2020
Debt Instrument [Line Items]
Principal amount			$ 3,387,000,000		$ 3,387,000,000						$ 3,127,000,000
Interest expense, net			$ 32,000,000	$ 33,000,000	$ 63,000,000	$ 66,000,000
Weighted-average interest rate of total debt			3.70%	4.20%	3.70%	4.20%		3.70%			3.70%	3.70%
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 | €								€ 445				€ 445
Principal amount			$ 524,000,000		$ 524,000,000						$ 518,000,000
5.500% Senior Notes due 2026 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate		5.50%	5.50%		5.50%			5.50%
Principal amount			$ 325,000,000		$ 325,000,000						325,000,000
5.500% Senior Notes due 2026 | Acquisition Corp. | Subsequent Event
Debt Instrument [Line Items]
Interest rate	5.50%
Debt instrument remaining outstanding amount	$ 343,000,000
Redemption price, percentage of principal amount redeemed	102.75%
2.750% Senior Secured Notes due 2028 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate			2.75%		2.75%			2.75%
Face or principal amount of debt instrument | €								€ 325				€ 325
Principal amount			$ 383,000,000		$ 383,000,000						379,000,000
3.875% Senior Secured Notes due 2030 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate			3.875%		3.875%			3.875%	3.875%
Principal amount			$ 535,000,000		$ 535,000,000						535,000,000
3.000% Senior Secured Notes due 2031
Debt Instrument [Line Items]
Interest rate			3.00%	3.00%	3.00%	3.00%		3.00%
3.000% Senior Secured Notes due 2031 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate			3.00%		3.00%			3.00%	3.00%	3.00%			3.00%
Face or principal amount of debt instrument										$ 250,000,000
Principal amount			$ 800,000,000		$ 800,000,000						$ 550,000,000
Senior Term Loan Facility
Debt Instrument [Line Items]
Debt fees									$ 3,000,000
Capitalized debt fees									$ 1,000,000
Senior Term Loan Facility | Acquisition Corp.
Debt Instrument [Line Items]
Line of credit facility, increase		$ 325,000,000
Maximum commitments under the facility		$ 1,145,000,000
Senior Term Loan Facility | Acquisition Corp. | Subsequent Event
Debt Instrument [Line Items]
Face or principal amount of debt instrument	$ 1,145,000,000						$ 325,000,000
2.750% Senior Secured Notes due 2028 | Acquisition Corp.
Debt Instrument [Line Items]
Interest rate									2.75%
Senior Notes
Debt Instrument [Line Items]
Scheduled maturities of long-term debt in 2021			0		0
Scheduled maturities of long-term debt in 2022			0		0
Scheduled maturities of long-term debt in 2023			0		0
Scheduled maturities of long-term debt in 2024			0		0
Scheduled maturities of long-term debt, 2025			0		0
Scheduled maturities of long-term debt, 2026			849,000,000		849,000,000
Scheduled maturities of long-term debt, thereafter			$ 1,718,000,000		$ 1,718,000,000