Derivative Financial Instruments - FGL's Exposure to Credit Loss on Call Options Held (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2015	Sep. 30, 2014
Derivatives, Fair Value [Line Items]
Notional Amount	$ 9,192.8	$ 7,602.6
Bank of America
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/*/A
Notional Amount	$ 2,233.3	2,239.9
Deutsche Bank
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	*/A1/A
Notional Amount	$ 2,481.4	2,810.0
Morgan Stanley
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/A3/BBB+
Notional Amount	$ 4,086.2	2,294.7
Barclay's Bank
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/A2/A-
Notional Amount	$ 391.9	258.0
Call options
Derivatives, Fair Value [Line Items]
Fair Value	80.7	296.3
Collateral	(7.0)	(188.0)
Net Credit Risk	73.7	108.3
Derivatives not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Fair Value	106.0	324.1
Derivatives \| Derivatives not designated as hedging instrument \| Call options
Derivatives, Fair Value [Line Items]
Fair Value	80.7	296.3
Derivatives \| Derivatives not designated as hedging instrument \| Call options \| Bank of America
Derivatives, Fair Value [Line Items]
Fair Value	16.5	92.7
Collateral	0.0	(52.5)
Net Credit Risk	16.5	40.2
Derivatives \| Derivatives not designated as hedging instrument \| Call options \| Deutsche Bank
Derivatives, Fair Value [Line Items]
Fair Value	26.0	108.0
Collateral	0.0	(72.5)
Net Credit Risk	26.0	35.5
Derivatives \| Derivatives not designated as hedging instrument \| Call options \| Morgan Stanley
Derivatives, Fair Value [Line Items]
Fair Value	34.8	85.0
Collateral	(7.0)	(63.0)
Net Credit Risk	27.8	22.0
Derivatives \| Derivatives not designated as hedging instrument \| Call options \| Barclay's Bank
Derivatives, Fair Value [Line Items]
Fair Value	3.4	10.6
Collateral	0.0	0.0
Net Credit Risk	$ 3.4	$ 10.6

Derivative instrument credit rating.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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- Definition

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 20

-Section 50

-Paragraph 4D

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=51814546&loc=SL51823488-111719

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- Definition

Fair value, after effects of master netting arrangements, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset offset against an obligation to return collateral. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=d3e41678-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226016-175313

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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