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, 2013	Sep. 30, 2012
Derivatives, Fair Value [Line Items]
Notional Amount	$ 6,183.2	$ 5,830.4
Fair Value	262.6	200.7
Bank of America [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	Baa2/A-
Notional Amount	1,936.9	1,884.0
Deutsche Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A+
Notional Amount	1,723.0	1,816.5
Morgan Stanley [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	Baa1/A-
Notional Amount	1,938.6	1,634.7
Royal Bank of Scotland [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	Baa1/A-
Notional Amount	468.0	353.9
Barclay's Bank [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A+
Notional Amount	116.7	131.3
Credit Suisse [Member]
Derivatives, Fair Value [Line Items]
Credit Rating (Moody's/S&P)	A2/A
Notional Amount	0	10.0
Call options [Member]
Derivatives, Fair Value [Line Items]
Fair Value	262.0	200.7
Derivatives Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair Value	266.0	203.9
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member]
Derivatives, Fair Value [Line Items]
Fair Value	262.0	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	81.0	64.1
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Deutsche Bank [Member]
Derivatives, Fair Value [Line Items]
Fair Value	69.6	61.7
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Morgan Stanley [Member]
Derivatives, Fair Value [Line Items]
Fair Value	80.3	51.6
Derivatives [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Call options [Member] | Royal Bank of Scotland [Member]
Derivatives, Fair Value [Line Items]
Fair Value	27.7	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	3.4	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