Goodwill and Intangibles, including DAC and VOBA - Summary of Changes in Carrying Amounts of Goodwill and Intangible Assets Including FGL's DAC and VOBA Balances (Detail) (USD $)	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Goodwill	$ 1,524,800,000
Beginning Balance, Indefinite Lived Intangible Assets	1,215,900,000
Beginning Balance, Finite Lived Intangible Assets	917,200,000
Beginning Balance, Intangible Assets, Excluding Goodwill	2,683,700,000
Goodwill, Acquired During Period	7,100,000
Indefinite-lived Intangible Assets Acquired	4,000,000
Acquisitions (Note 13)	13,400,000
Goodwill, Impairment Loss	(28,300,000)
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)	(31,900,000)
Impairment of Intangible Assets, Finite-lived	60,200,000	0
Goodwill and Intangible Asset Impairment	(31,900,000)
Deferrals	95,500,000
Less: Components of amortization:
Amortization of intangibles	(31,800,000)	(43,400,000)
Adjustment for unrealized investment (gains), net, Goodwill	900,000
Effect of translation, Intangible Assets Excluding Goodwill	(17,500,000)
Ending Balance, Goodwill	1,491,900,000
Ending Balance, Indefinite Lived Intangible Assets	1,178,600,000
Ending Balance, Finite Lived Intangible Assets	898,000,000
Ending Balance, Intangible Assets, Excluding Goodwill	2,712,300,000
Unlocking [Member]
Less: Components of amortization:
Amortization of intangibles	(1,500,000)
Interest [Member]
Less: Components of amortization:
Amortization of intangibles	8,300,000
Periodic amortization [Member]
Less: Components of amortization:
Amortization of intangibles	(38,600,000)
Definite Lived Intangible Assets [Member]
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Finite Lived Intangible Assets	917,200,000
Acquisitions (Note 3), Finite-Lived Intangible Assets	9,400,000
Impairment of Intangible Assets, Finite-lived	0
Less: Components of amortization:
Amortization of intangibles	(20,500,000)	(20,200,000)
Effect of translation, Finite Lived intangible assets	(8,100,000)
Ending Balance, Finite Lived Intangible Assets	898,000,000
Definite Lived Intangible Assets [Member] | Periodic amortization [Member]
Less: Components of amortization:
Amortization of intangibles	(20,500,000)
VOBA [Member]
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Finite Lived Intangible Assets	86,800,000
Less: Components of amortization:
Amortization of intangibles	(4,000,000)	(13,200,000)
Adjustment for unrealized investment (gains), net, Goodwill	6,900,000
Ending Balance, Finite Lived Intangible Assets	89,700,000
VOBA [Member] | Unlocking [Member]
Less: Components of amortization:
Amortization of intangibles	600,000
VOBA [Member] | Interest [Member]
Less: Components of amortization:
Amortization of intangibles	3,000,000
VOBA [Member] | Periodic amortization [Member]
Less: Components of amortization:
Amortization of intangibles	(7,600,000)
DAC [Member]
Intangible Assets, Including Goodwill [Roll Forward]
Beginning Balance, Finite Lived Intangible Assets	463,800,000
Deferrals	95,500,000
Less: Components of amortization:
Amortization of intangibles	(7,300,000)	(10,000,000)
Adjustment for unrealized investment (gains), net, Goodwill	(6,000,000)
Ending Balance, Finite Lived Intangible Assets	546,000,000
DAC [Member] | Unlocking [Member]
Less: Components of amortization:
Amortization of intangibles	(2,100,000)
DAC [Member] | Interest [Member]
Less: Components of amortization:
Amortization of intangibles	5,300,000
DAC [Member] | Periodic amortization [Member]
Less: Components of amortization:
Amortization of intangibles	(10,500,000)
Goodwill [Member]
Less: Components of amortization:
Effect of translation, Finite Lived intangible assets	(11,700,000)
Indefinite Lived Intangible Assets [Member]
Less: Components of amortization:
Effect of translation, Finite Lived intangible assets	$ (9,400,000)