Other Assets - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Asset Backed Loans And Other Invested Assets Gross	$ 46.0	$ 274.6
Long-term debt	5,540.7	6,112.1
Equity Securities Holdings Exposure Amount of Single Issuer Greater than Stated Percentage of Total Investments				10.00%
Provision for Loan, Lease, and Other Losses	12.8	93.5	$ 1.5
Unrealized Amortized Cost On Securities	38.1
Investments, Unrealized Gains	14.1
Investments, Unrealized Losses	0.0
Available For Sale Securities Carrying Value	52.2
Prepaid Expense and Other Assets, Current	137.6	133.1
Asset Backed Loans And Other Invested Assets	35.0	226.7
Other Investments	0.0	52.2
Other assets (Note 13)	172.6	412.0
Salus Capital Partners LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Loan and Lease Losses, Loans Acquired	45.4
Provision for Loan, Lease, and Other Losses	30.8
Salus Capital Partners LLC | Radioshack [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt	250.0
Front Street RE (Cayman) Ltd. [Member] | Radioshack [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt		7.0
Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	30.1	79.8
Asset Backed Loans And Other Invested Assets Gross	30.1	99.2
Radioshack [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt		250.0
Financing Receivable, Allowance for Credit Losses, Period Increase (Decrease)	(19.2)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	18.0
Radioshack [Member] | Loan Participations and Assignments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt		50.0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	9.0
Radioshack [Member] | Non-Qualifying Participation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt		100.0
Radioshack [Member] | FGL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from Recoveries of Loans Previously Charged off	22.7
Radioshack [Member] | Salus Capital Partners LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt		93.0
Radioshack [Member] | Radioshack [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses, Write-downs	(52.6)	(51.1)	$ 0.0
Asset based loan receivables [Member] | Radioshack [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trading Securities	3.0
Asset based loan receivables [Member] | Radioshack [Member] | FGL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trading Securities	$ 1.5
Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage Of Accounts Receivable Major Customers	13.10%
Credit Concentration Risk [Member] | Asset based loan receivables [Member] | Salus Capital Partners LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage Of Accounts Receivable Major Customers	29.60%
Inventories [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Asset-based loan, Collateral Type, Percent	52.00%
Receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Asset-based loan, Collateral Type, Percent	12.00%
Other assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Asset-based loan, Collateral Type, Percent	36.00%
Apparel [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Asset Backed Loans And Other Invested Assets Gross	$ 18.8	$ 66.0
Fair Value, Concentration of Risk, All Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage Of Investments Fair Value In Relation To Invested Assets Portfolio		24.00%		40.90%