Fair Value Measurements - Schedule of Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions		Mar. 31, 2019	Sep. 30, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total		$ 38	$ (4)
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total		47	4
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total		(9)	(8)
Other Current Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Foreign Currency Forward Exchange Contracts	[1],[2]	2
Other Current Assets | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Foreign Currency Forward Exchange Contracts	[2]	2
Other Current Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contractual Obligations	[3]	(3)	(2)
Other Current Liabilities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contractual Obligations	[3]	(3)	(2)
Other Noncurrent Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Foreign Currency Forward Exchange Contracts	[4]		4
Equity Method Investment	[5]	50
Interest rate swap	[6]		4
Other Noncurrent Assets | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Method Investment	[5]	50
Interest rate swap	[6]		4
Other Non-Current Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contractual Obligations	[3]	(6)	(6)
Interest rate swap	[6]	(5)
Other Non-Current Liabilities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest rate swap	[6]	(5)
Other Non-Current Liabilities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contractual Obligations	[3]	$ (6)	$ (6)

[1] $6 million and $4 million of foreign exchange derivative contracts in asset and liability positions, respectively, and $5 million of interest rate swap in a liability position including non-designated cash flow hedges.

[2] The fair value of foreign currency forward exchange contracts is based on dealer quotes of market forward rates and reflects the amount that the Company would receive or pay at their maturity dates for contracts involving the same currencies and maturity dates.

[3] This represents purchase obligations and contingent consideration related to the Company’s various acquisitions. This is based on a probability weighted performance approach and it is adjusted to fair value on a recurring basis and any adjustments are included as a component of operating income in the statement of operations. These amounts were mainly calculated using unobservable inputs such as future earnings performance of the Company’s various acquisitions and the expected timing of the payment

[4] $4 million of interest rate swap in an asset position.

[5] The fair value of equity method investment represents an equity method investment acquired during the six months March 31, 2019 whereby the Company has elected the fair value option under ASC 825 – Financial Instruments.  The valuation is based upon quoted prices in active markets and model-based valuation techniques to determine fair value

[6] The fair value of the interest rate swap is based on dealer quotes of market forward rates and reflects the amount that the Company would receive or pay as of March 31, 2019 for contracts involving the same attributes and maturity dates.