Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended
Mar. 31, 2017	Sep. 30, 2016
Commitment And Contingencies [Line Items]
Long-term Debt	$ 5,727.0	$ 5,540.7
Maximum [Member]
Commitment And Contingencies [Line Items]
Expiry date of remainder part of notional amount	1 year
Fidelity And Guaranty Life Holdings [Member]
Commitment And Contingencies [Line Items]
Loss Contingency Accrual, Insurance-related Assessment, Premium Tax Offset	$ 2.2
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability	2.1
FGL [Member]
Commitment And Contingencies [Line Items]
Expiration of partial amount of unfunded, legally binding lending commitments	210.7
Cressy Plaintiff [Member]
Commitment And Contingencies [Line Items]
Litigation Settlement, Amount	1.3
Loss Contingency Accrual, Provision	9.2
Estimated Litigation Liability	0.1
Eddie L. Cressy v. Fidelity Guaranty [sic] Life Insurance Company, et. al. [Member]
Commitment And Contingencies [Line Items]
Legal Fees	6.0
Litigation Settlement, Expense	3.2
Asset based loan receivables [Member] \| Salus Capital Partners L L C [Member]
Commitment And Contingencies [Line Items]
Expiration of partial amount of unfunded, legally binding lending commitments	$ 3.8

Commitment And Contingencies [Line Items]

No definition available.

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- Definition

Partially amount of notional amount of unfunded, legally binding lending commitments.

+ References

No definition available.

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Expiry date of remainder part of notional amount.

+ References

No definition available.

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- Definition

The amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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- Definition

Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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- Definition

Amount of judgment or settlement awarded to (against) the entity in respect of litigation.

+ References

No definition available.

+ Details

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- Definition

Amount of litigation expense, including but not limited to legal, forensic, accounting, and investigative fees.

+ References

No definition available.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The amount of insurance-related assessment liability that is expected to be recovered through a premium tax offset based on current laws applied to in-force policies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 405
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392405&loc=d3e24119-109301

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- Definition

Amount charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

+ References

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- Definition

The liability as of the balance sheet date representing required funding mandated by statute or regulatory authority that is related directly or indirectly to underwriting activities, including pools for self-insurance and excluding premium taxes and income taxes. The funds derived from the assessments generally enable a government guarantor to pay insurance claims in the event that the underwriting insurer is insolvent or otherwise unable to meet its payment obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 405
-SubTopic 30
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-URI http://asc.fasb.org/extlink&oid=51828112&loc=d3e23169-109297

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