Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013 Investment industry	Dec. 31, 2012	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Other Than Temporary Impairment Credit Losses Recognized In Earnings Additions Change Of Intent Operations		$ 0
Document Period End Date	Dec. 31, 2013
Available For Sale Securities Gross Unrealized Losses Investment	280.1		263.9
Other than temporary impairment credit losses recognized in earnings additions other		0.5
Other Than Temporary Impairment Credit Losses Recognized In Earnings Additions Including Credit Impairments		0
Amortized cost on other-than temporary impairments	0.2		1.6
Fair value on other than temporary impairments	0.2		1.1
Change-of-intent, and non-credit losses in other comprehensive income		1.5
Significant investment, number of industries	1
Industry holdings, number of top investments	10
Equity Securities Holdings Exposure Amount of Single Issuer Greater than Stated Percentage of Total Investments	37.80%
Non-agency residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains included in AOCI related to the non-credit portion of other than-temporary impairments on non-agency residential-mortgage-backed securities	0.9
Unrealized losses included in AOCI related to the non-credit portion of other than-temporary impairments on non-agency residential-mortgage-backed securities	1.9		(1.9)
Available For Sale Securities Gross Unrealized Losses Investment	11.3		13.4
Other Marketable Securities, Current	13,727.8		19.4
FGL [Member] | Stockholders' Equity, Total [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of investment	2,925.5		1,983.7
Percentage of fair value of the invested assets portfolio	16.90%		12.00%
Investment in issuers	34		19
Percentage of stockholders equity	10.00%
Net Investment Income [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Losses	0	0
Available for sale securities on fixed maturity	1,705.9	0
Available-for-sale Securities, Gross Realized Gains	0	0
Concentration [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Securities Held by Subsidiaries Subject to Specialized Industry Accounting Principles at Fair Value	1,974.0		1,892.1
Percentage of fair value of the invested assets portfolio	11.50%		11.70%
Number Of Issuers In Investment	82
Concentration [Member] | FGL [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of investment	140.5		150.7
Percentage of fair value of the invested assets portfolio	1.00%
Insurance and Financial Services [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value on securities	77.1		60.9
Percentage of amortized cost	20.00%
Percentage of carrying values of all investments (less than 1%)	1.00%
FHLB of Atlanta Funding Agreement Collateral Held [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Owned, at Fair Value	$ 591.8		$ 604.9