Subsequent Events - Additional Information (Detail)					6 Months Ended	12 Months Ended
	Apr. 30, 2019 EUR (€)	Apr. 16, 2019	Nov. 05, 2018	Oct. 09, 2018 EUR (€)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Oct. 12, 2018	Mar. 31, 2018
Subsequent Event [Line Items]
Face or principal amount of debt instrument | $					$ 3,022,000,000	$ 2,851,000,000
5.625% Senior Secured Notes
Subsequent Event [Line Items]
Interest rate					5.625%			5.625%
5.625% Senior Secured Notes | Acquisition Corp.
Subsequent Event [Line Items]
Interest rate			5.625%		5.625%	5.625%
Due date of senior secured notes			2022		2022	2022
Face or principal amount of debt instrument | $					$ 221,000,000	$ 248,000,000
5.625% Senior Secured Notes | Subsequent
Subsequent Event [Line Items]
Interest rate		5.625%
Due date of senior secured notes		2022
Debt settlement date		May 16, 2019
3.625% Senior Secured Notes due 2026
Subsequent Event [Line Items]
Interest rate					3.625%
3.625% Senior Secured Notes due 2026 | Acquisition Corp.
Subsequent Event [Line Items]
Interest rate				3.625%	3.625%		3.625%
Due date of senior secured notes				2026	2026
Face or principal amount of debt instrument | €				€ 250,000,000
3.625% Senior Secured Notes due 2026 | Subsequent | Acquisition Corp.
Subsequent Event [Line Items]
Interest rate	3.625%
Due date of senior secured notes	2026
Face or principal amount of debt instrument | €	€ 195,000,000