Derivative Financial Instruments - FGL's Exposure to Credit Loss on Call Options Held (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Jun. 30, 2014	Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Document Period End Date	Jun. 30, 2014
Derivative, Notional Amount	$ 7,163.3	$ 6,407.4
Bank of America [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/*/A
Derivative, Notional Amount	2,150.9	2,037.8
Deutsche Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	*/A3/A
Derivative, Notional Amount	2,116.6	1,620.4
Morgan Stanley [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A+/A2/A
Derivative, Notional Amount	2,639.8	2,264.1
Royal Bank of Scotland [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A-/*/A-
Derivative, Notional Amount	0	364.3
Barclay's Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A/A2/A
Derivative, Notional Amount	256.0	120.8
Call options [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	115.3	149.8
Derivative Asset, Fair Value, Gross Asset	324.6	221.8
Derivative Asset, Collateral, Obligation to Return Cash, Offset	209.3	72.0
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	338.6	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	324.6	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	43.2	70.7
Derivative Asset, Fair Value, Gross Asset	100.4	70.7
Derivative Asset, Collateral, Obligation to Return Cash, Offset	57.2	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	38.4	28.7
Derivative Asset, Fair Value, Gross Asset	98.1	51.7
Derivative Asset, Collateral, Obligation to Return Cash, Offset	76.5	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	22.5	26.7
Derivative Asset, Fair Value, Gross Asset	114.9	75.7
Derivative Asset, Collateral, Obligation to Return Cash, Offset	75.6	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	0	20.3
Derivative Asset, Fair Value, Gross Asset	0	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	11.2	3.4
Derivative Asset, Fair Value, Gross Asset	11.2	3.4
Derivative Asset, Collateral, Obligation to Return Cash, Offset	$ 0	$ 0