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, 2013	Sep. 30, 2012
Derivatives, Fair Value [Line Items]
Document Period End Date	Jun. 30, 2013
Derivative, Notional Amount	$ 6,293.2	$ 5,830.4
Fair Value	227.4	200.7
Bank of America [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	Baa2/A-
Derivative, Notional Amount	2,098.4	1,884.0
Deutsche Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	Baa1/A-
Derivative, Notional Amount	2,024.7	1,634.7
Morgan Stanley [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A+
Derivative, Notional Amount	1,564.0	1,816.5
Royal Bank of Scotland [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	Baa1/A-
Derivative, Notional Amount	479.0	353.9
Barclay's Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A+
Derivative, Notional Amount	127.1	131.3
Credit Suisse [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A
Derivative, Notional Amount	0	10.0
Call options [Member]
Derivatives, Fair Value [Line Items]
Fair Value	227.4	200.7
Derivatives Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair Value	237.6	203.9
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member]
Derivatives, Fair Value [Line Items]
Fair Value	227.4	200.7
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Bank of America [Member]
Derivatives, Fair Value [Line Items]
Fair Value	76.4	64.1
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Deutsche Bank [Member]
Derivatives, Fair Value [Line Items]
Fair Value	64.5	51.6
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Morgan Stanley [Member]
Derivatives, Fair Value [Line Items]
Fair Value	57.4	61.7
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Royal Bank of Scotland [Member]
Derivatives, Fair Value [Line Items]
Fair Value	24.6	19.6
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Barclay's Bank [Member]
Derivatives, Fair Value [Line Items]
Fair Value	4.5	3.1
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Credit Suisse [Member]
Derivatives, Fair Value [Line Items]
Fair Value	$ 0	$ 0.6