Derivative Financial Instruments - FGL's Exposure to Credit Loss on Call Options Held (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Mar. 31, 2014	Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Document Period End Date	Mar. 31, 2014
Derivative, Notional Amount	$ 6,801.9	$ 6,407.4
Derivative Asset, Fair Value, Gross Asset	273.0	221.8
Bank of America [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/A
Derivative, Notional Amount	2,018.2	2,037.8
Deutsche Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A3/A
Derivative, Notional Amount	2,143.3	1,620.4
Morgan Stanley [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A
Derivative, Notional Amount	2,265.3	2,264.1
Royal Bank of Scotland [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	BBB+/Baa2
Derivative, Notional Amount	114.7	364.3
Barclay's Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A
Derivative, Notional Amount	260.4	120.8
Call options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	121.5	149.8
Derivative Asset, Fair Value, Gross Asset	271.5	221.8
Derivative Asset, Collateral, Obligation to Return Cash, Offset	150.0	72.0
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	276.7	227.7
Derivatives For Trading And Investment [Member] | Not Designated as Hedging Instrument [Member] | Call options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	271.5	221.8
Derivatives For Trading And Investment [Member] | Not Designated as Hedging Instrument [Member] | Call options [Member] | Bank of America [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	41.9	70.7
Derivative Asset, Fair Value, Gross Asset	83.0	70.7
Derivative Asset, Collateral, Obligation to Return Cash, Offset	41.1	0
Derivatives For Trading And Investment [Member] | Not Designated as Hedging Instrument [Member] | Call options [Member] | Deutsche Bank [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	36.2	28.7
Derivative Asset, Fair Value, Gross Asset	89.9	51.7
Derivative Asset, Collateral, Obligation to Return Cash, Offset	45.7	23.0
Derivatives For Trading And Investment [Member] | Not Designated as Hedging Instrument [Member] | Call options [Member] | Morgan Stanley [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	26.7	26.7
Derivative Asset, Fair Value, Gross Asset	81.9	75.7
Derivative Asset, Collateral, Obligation to Return Cash, Offset	63.2	49.0
Derivatives For Trading And Investment [Member] | Not Designated as Hedging Instrument [Member] | Call options [Member] | Royal Bank of Scotland [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	8.1	20.3
Derivative Asset, Fair Value, Gross Asset	8.1	20.3
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Derivatives For Trading And Investment [Member] | Not Designated as Hedging Instrument [Member] | Call options [Member] | Barclay's Bank [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	8.6	3.4
Derivative Asset, Fair Value, Gross Asset	8.6	3.4
Derivative Asset, Collateral, Obligation to Return Cash, Offset	$ 0	$ 0