Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended		15 Months Ended
	Jun. 30, 2013 Investment industry	Jun. 30, 2013 Investment industry	Jul. 01, 2012	Jul. 01, 2013	Sep. 30, 2012	Jan. 01, 2012
Schedule of Available-for-sale Securities [Line Items]
Document Period End Date		Jun. 30, 2013
Treasury Yield	2.48%	2.48%			1.63%
Other than temporary impairment credit losses recognized in earnings additions other	$ 0.7	$ 1.6	$ 19.8	$ 2.5
Credit losses in operations, including credit impairments	0.5	0.8
Credit losses in operations, change of intent operations	0.2	0.9	15.0	1.8
Amortized cost on other-than temporary impairments	4.1	4.1				101.9
Fair value on other than temporary impairments	2.4	2.4				80.6
Change-of-intent, and non-credit losses in other comprehensive income		0	2.6	0.7
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	0.7	1.6	19.8	2.5
Significant investment, number of industries	1	1
Industry holdings, number of top investments	10	10
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	0			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	0	0			1.9
Other Marketable Securities, Current	0	0			0
FGL [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of investment	1,944.6	1,944.6
Percentage of fair value of the invested assets portfolio	11.80%	11.80%
Investment in issuers	78	78
Percentage of investment accounting	34.90%	34.90%
FGL [Member] | Stockholders' Equity, Total [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of investment	1,629.2	1,629.2			1,625.9
Percentage of fair value of the invested assets portfolio	10.00%	10.00%			9.80%
Investment in issuers					13
Percentage of stockholders equity	10.00%	10.00%
Net Investment Income [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities on fixed maturity	836.0	5,741.6	4,366.3	1,216.2
Available-for-sale Securities, Gross Realized Gains	35.0	284.0	211.9	49.5
Available-for-sale Securities, Gross Realized Losses	(0.5)	1.0	20.9	9.2
Concentration [Member] | FGL [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of investment	156.9	156.9			152.9
Percentage of fair value of the invested assets portfolio	1.00%	1.00%			0.70%
Insurance and Financial Services [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value on securities	$ 25.4	$ 25.4			$ 1.2
Percentage of amortized cost		20.00%
Percentage of carrying values of all investments (less than 1%)		1.00%