Acquisitions - Armored AutoGroup acquisition (Detail) - USD ($) $ / shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	May 21, 2015	Sep. 30, 2013
Business Acquisition [Line Items]
Goodwill (Note 12)	$ 2,478.4	$ 2,487.4			$ 1,524.8
AAG Acquisition [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue		4,985.5	$ 5,078.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	30.9
Goodwill (Note 12)	975.4
Business Combination, Consideration Transferred	929.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	156.5
Inventory	82.5
Property, plant and equipment	37.6
Goodwill (Note 12)	418.0			$ 418.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	24.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	(119.2)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	(540.0)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	(137.1)
Business Acquisition, Pro Forma Net Income (Loss)		$ (517.5)	$ (71.4)
Business Acquisition, Pro Forma Earnings Per Share, Basic		$ (2,610)	$ (440)
Pro forma diluted net income per common share (in dollars per share)		$ (2,610)	$ (440)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	$ 929.3
Tradenames Trademarks And Patents [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)				295.0
Technology-Based Intangible Assets [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)				41.0
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Licensing Agreements [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)				19.0
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Customer Relationships [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Goodwill (Note 12)				$ 63.0
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	15 years
Share-based compensation [Member] | AAG Acquisition [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustments [Table Text Block]	10.4