Derivative Financial Instruments - Fair Value of Outstanding Derivative Contracts in Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2014
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	$ 2.6	$ 8.5
Total liability derivatives	9.8	3.0
Derivatives designated as hedging instruments [Member] | Interest Rate Contract [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives			$ 0.0
Derivatives designated as hedging instruments [Member] | Interest Rate Contract [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.0	0.7
Derivatives designated as hedging instruments [Member] | Interest Rate Contract [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	1.0	0.4
Derivatives designated as hedging instruments [Member] | Commodity Swap And Option Agreements [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	2.1	2.9
Derivatives designated as hedging instruments [Member] | Commodity Swap And Option Agreements [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.2	0.0
Derivatives designated as hedging instruments [Member] | Foreign Exchange Forward [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.0	0.1
Derivatives designated as hedging instruments [Member] | Foreign Exchange Contract [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.1	5.5
Derivatives designated as hedging instruments [Member] | Foreign Exchange Contract [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	7.6	1.7
Derivatives designated as hedging instruments [Member] | Foreign Exchange Contract [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	1.1	0.1
Derivatives designated as hedging instruments [Member] | Commodity contracts [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	0.1	0.1
Derivatives designated as hedging instruments [Member] | Interest Rate Swap [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives		0.2
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	2.9	8.7
Total liability derivatives	10.8	3.2
Not Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member] | Accounts payable and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Total liability derivatives	1.0	0.2
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Receivables, net [Member]
Derivatives, Fair Value [Line Items]
Total asset derivatives	0.3	0.2
Fair Value, Measurements, Recurring [Member]
Derivatives, Fair Value [Line Items]
Assets, Fair Value Disclosure, Recurring	2.9	8.7
Liabilities, Fair Value Disclosure, Recurring	10.8	3.2
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Derivatives, Fair Value [Line Items]
Assets, Fair Value Disclosure, Recurring	0.0	0.0
Liabilities, Fair Value Disclosure, Recurring	0.0	0.0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivatives, Fair Value [Line Items]
Assets, Fair Value Disclosure, Recurring	2.9	8.7
Liabilities, Fair Value Disclosure, Recurring	10.8	3.2
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Derivatives, Fair Value [Line Items]
Assets, Fair Value Disclosure, Recurring	0.0	0.0
Liabilities, Fair Value Disclosure, Recurring	$ 0.0	$ 0.0