Goodwill and Intangibles, including DAC and VOBA - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended					6 Months Ended			6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 VOBA [Member]	Mar. 31, 2013 VOBA [Member]	Sep. 30, 2013 VOBA [Member]	Mar. 31, 2014 DAC [Member]	Mar. 31, 2013 DAC [Member]	Sep. 30, 2013 DAC [Member]	Mar. 31, 2014 Minimum [Member]	Mar. 31, 2014 Maximum [Member]	Mar. 31, 2014 Weighted Average [Member] VOBA [Member]	Mar. 31, 2014 Hardware Acquisition [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill, Acquired During Period			$ 10.5											$ 3.5
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	82.0		82.0		20.7
Intangible assets amortization method			straight-line method
Weighted average amortization period											1 year	20 years	4 years 9 months 18 days
Cumulative adjustments for net unrealized investment gains					(144.5)		(81.4)	(23.5)		18.6
Amortization of intangibles	37.4	49.0	80.8	135.6	24.1	75.7		16.0	22.7
Deferred sales inducements, net of shadow adjustments								29.5		26.2
2014	80.7		80.7		44.5
2015	80.7		80.7		39.7
2016	80.7		80.7		32.5
2017	$ 80.7		$ 80.7		$ 26.1