Basis of Preparation and Nature of Operations Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Number of reporting segments	2
Common Stock, Par or Stated Value Per Share			$ 0.01
Long-term debt	$ 5,404.2	$ 5,801.9
Document Period End Date	Mar. 31, 2018
HGI Energy Holdings, LLC [Member] | Zero point seven one percent [Member] | Secured Debt [Member]
Business Acquisition [Line Items]
Long-term debt, interest rate		1.50%
Long-term debt		$ 92.0
Front Street Re (Delaware) Ltd. [Member]
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses	$ 65.0
Deposit Liabilities, Description	6.5
Spectrum Brands [Member]
Business Acquisition [Line Items]
Percentage Of Ownership Interest	62.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	38.00%
Spectrum Brands [Member] | Four Point Zero Percent Senior Notes [Member] | Secured Debt [Member]
Business Acquisition [Line Items]
Long-term debt, interest rate	4.00%
HGI | 7.875% Senior Secured Notes, due July 15, 2019
Business Acquisition [Line Items]
Redemption Price Of Debt Instrument To Percentage Of Principal Amount	100.00%
Long-term Debt and Capital Lease Obligations, Maturities, Repayments of Principal in Year Two	$ 0.0
HGI | 7.875% Senior Secured Notes, due July 15, 2019 | Secured Debt [Member]
Business Acquisition [Line Items]
Long-term debt, interest rate	0.00%	7.875%
Long-term Debt, Maturities, Repayments of Principal in Year Five		$ 864.4
FS Holdco II Ltd. [Domain]
Business Acquisition [Line Items]
Business Combination, Assets and Liabilities Arising from Contingencies, Amount Recognized, Net	$ 26.6
FGL [Member] | CF Corporation [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price	$ 31.10