Goodwill and Intangibles, including DAC and VOBA, net - Summary of Changes in Carrying Amounts of Goodwill and Intangible Assets Including FGL's DAC and VOBA Balances (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Goodwill	$ 1,476.7	$ 694.2
Beginning Balance, Indefinite Lived Intangible Assets	1,178.1	841.1
Beginning Balance, Finite Lived Intangible Assets	985.1
Beginning Balance, Intangible Assets, Excluding Goodwill	2,729.1	1,988.5
Goodwill, Acquired During Period	65.8	786.6
Acquisitions (Note 3), Indefinite Lived Intangible Assets	46.7	331.0
Acquisitions (Note 13)	70.2	519.3
Deferrals	239.0	147.4
Less: Components of amortization:
Amortization of Intangible Assets	(179.2)	(260.1)	(224.3)
Adjustment for unrealized investment (gains), net, Goodwill	(156.8)	327.3
Effect of translation, Goodwill	(17.7)	(4.1)
Effect of translation, Indefinite Lived intangible assets	(8.9)	6.0
Effect of translation, Intangible Assets Excluding Goodwill	(18.6)	6.7
Ending Balance, Goodwill	1,524.8	1,476.7	694.2
Ending Balance, Indefinite Lived Intangible Assets	1,215.9	1,178.1	841.1
Ending Balance, Finite Lived Intangible Assets	917.2	985.1
Ending Balance, Intangible Assets, Excluding Goodwill	2,683.7	2,729.1	1,988.5
Periodic amortization
Less: Components of amortization:
Goodwill Amortization
Indefinite Lived Intangible Assets, Amortization
Amortization of Intangible Assets	(232.1)	(334.5)
Interest
Less: Components of amortization:
Goodwill Amortization
Indefinite Lived Intangible Assets, Amortization
Amortization of Intangible Assets	28.6	31.3
Unlocking
Less: Components of amortization:
Goodwill Amortization
Indefinite Lived Intangible Assets, Amortization
Amortization of Intangible Assets	24.3	43.1
Goodwill
Intangible Assets, Including Goodwill [Roll Forward]
Deferrals
Less: Components of amortization:
Adjustment for unrealized investment (gains), net, Goodwill
Definite Lived Intangible Assets
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Finite Lived Intangible Assets	985.1	873.9
Acquisitions (Note 3), Finite-Lived Intangible Assets	23.5	188.3
Deferrals
Less: Components of amortization:
Amortization of Intangible Assets	(81.7)	(77.8)	(63.7)
Adjustment for unrealized investment (gains), net, Goodwill
Effect of translation, Finite Lived intangible assets	(9.7)	0.7
Ending Balance, Finite Lived Intangible Assets	917.2	985.1	873.9
Definite Lived Intangible Assets | Periodic amortization
Less: Components of amortization:
Amortization of Intangible Assets	(81.7)	(77.8)
Definite Lived Intangible Assets | Interest
Less: Components of amortization:
Amortization of Intangible Assets
Definite Lived Intangible Assets | Unlocking
Less: Components of amortization:
Amortization of Intangible Assets
VOBA
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Finite Lived Intangible Assets	225.3	104.3
Acquisitions (Note 3), Finite-Lived Intangible Assets
Deferrals
Less: Components of amortization:
Amortization of Intangible Assets	(55.8)	(137.0)	(145.5)
Adjustment for unrealized investment (gains), net, Goodwill	(82.7)	258.0
Effect of translation, Finite Lived intangible assets
Ending Balance, Finite Lived Intangible Assets	86.8	225.3	104.3
VOBA | Periodic amortization
Less: Components of amortization:
Amortization of Intangible Assets	(92.4)	(194.6)
VOBA | Interest
Less: Components of amortization:
Amortization of Intangible Assets	15.0	21.8
VOBA | Unlocking
Less: Components of amortization:
Amortization of Intangible Assets	21.6	35.8
DAC
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Finite Lived Intangible Assets	340.6	169.2
Acquisitions (Note 3), Finite-Lived Intangible Assets
Deferrals	239.0	147.4
Less: Components of amortization:
Amortization of Intangible Assets	(41.7)	(45.3)	(15.2)
Adjustment for unrealized investment (gains), net, Goodwill	(74.1)	69.3
Effect of translation, Finite Lived intangible assets
Ending Balance, Finite Lived Intangible Assets	463.8	340.6	169.2
DAC | Periodic amortization
Less: Components of amortization:
Amortization of Intangible Assets	(58.0)	(62.1)
DAC | Interest
Less: Components of amortization:
Amortization of Intangible Assets	13.6	9.5
DAC | Unlocking
Less: Components of amortization:
Amortization of Intangible Assets	2.7	7.3
Indefinite Lived Intangible Assets
Intangible Assets, Including Goodwill [Roll Forward]
Deferrals
Less: Components of amortization:
Adjustment for unrealized investment (gains), net, Goodwill