Derivative Financial Instruments - FGL's Exposure to Credit Loss on Call Options Held (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Notional Amount	$ 7,602.6	$ 6,407.4
Bank of America
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/*/A
Notional Amount	2,239.9	2,037.8
Deutsche Bank
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	*/A3/A
Notional Amount	2,294.7	1,620.4
Morgan Stanley
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A+/A3/A
Notional Amount	2,810.0	2,264.1
Royal Bank of Scotland
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A-/*/A-
Notional Amount	0	364.3
Barclay's Bank
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/A2/A-
Notional Amount	258.0	120.8
Call options
Derivatives, Fair Value [Line Items]
Fair Value	296.3	221.8
Collateral	188.0	72.0
Net Credit Risk	108.3	149.8
Derivatives not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Fair Value	324.1	227.7
Derivatives | Derivatives not designated as hedging instrument | Call options
Derivatives, Fair Value [Line Items]
Fair Value	296.3	221.8
Derivatives | Derivatives not designated as hedging instrument | Call options | Bank of America
Derivatives, Fair Value [Line Items]
Fair Value	92.7	70.7
Collateral	52.5	0
Net Credit Risk	40.2	70.7
Derivatives | Derivatives not designated as hedging instrument | Call options | Deutsche Bank
Derivatives, Fair Value [Line Items]
Fair Value	108.0	51.7
Collateral	72.5	23.0
Net Credit Risk	35.5	28.7
Derivatives | Derivatives not designated as hedging instrument | Call options | Morgan Stanley
Derivatives, Fair Value [Line Items]
Fair Value	85.0	75.7
Collateral	63.0	49.0
Net Credit Risk	22.0	26.7
Derivatives | Derivatives not designated as hedging instrument | Call options | Royal Bank of Scotland
Derivatives, Fair Value [Line Items]
Fair Value	0	20.3
Collateral	0	0
Net Credit Risk	0	20.3
Derivatives | Derivatives not designated as hedging instrument | Call options | Barclay's Bank
Derivatives, Fair Value [Line Items]
Fair Value	10.6	3.4
Collateral	0	0
Net Credit Risk	$ 10.6	$ 3.4