Derivative Financial Instruments - FGL's Exposure to Credit Loss on Call Options Held (Detail) - USD ($) $ in Millions		9 Months Ended
Dec. 31, 2017	Sep. 30, 2018
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)	A/*/A+
Fair Value		$ 449
Merrill Lynch
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)		A+/*/A+
Deutsche Bank
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)	A-/A3/A-	A-/A3/BBB+
Notional Amount	$ 1,345	$ 1,286
Fair Value	51	46
Collateral	55	47
Net Credit Risk	$ (4)	$ (1)
Morgan Stanley
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)	*/A1/A+	*/A1/A+
Notional Amount	$ 1,555	$ 1,969
Fair Value	92	66
Collateral	101	72
Net Credit Risk	$ (9)	$ (6)
Barclay's Bank
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)	A*+/A1/A	A/Baa3/BBB
Notional Amount	$ 2,090	$ 1,387
Fair Value	103	65
Collateral	95	42
Net Credit Risk	$ 8	$ 23
Canadian Imperial Bank of Commerce [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)	AA-/Aa3/A+	*/Aa2/A+
Notional Amount	$ 2,807	$ 2,376
Fair Value	96	81
Collateral	98	82
Net Credit Risk	(2)	$ (1)
Wells Fargo [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)		A+/A2/A-
Notional Amount		$ 1,063
Fair Value		37
Collateral		37
Net Credit Risk		$ 0
GOLDMAN SACH MTF [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Fitch/Moody's/S&P) (a)		A/A3/BBB+
Notional Amount		$ 309
Fair Value		7
Collateral		8
Net Credit Risk		(1)
Derivatives For Trading And Investment \| Not Designated as Hedging Instrument \| Call options
Derivatives, Fair Value [Line Items]
Notional Amount	10,577	11,905
Fair Value	492	431
Collateral	467	377
Net Credit Risk	25	54
Derivatives For Trading And Investment \| Not Designated as Hedging Instrument \| Call options \| Merrill Lynch
Derivatives, Fair Value [Line Items]
Notional Amount	2,780	3,515
Fair Value	150	129
Collateral	118	89
Net Credit Risk	$ 32	$ 40

Derivative instrument credit rating.

No definition available.

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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

+ Details

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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=84234895&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&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=82924980&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=84234895&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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=82849420&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.

+ Details

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