Goodwill and Intangibles, including DAC and VOBA - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill, Acquired During Period	$ 3.5
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	80.7
Intangible assets amortization method	straight-line method
Amortization of intangibles	43.4	86.6
2014	80.7
2015	80.7
2016	80.7
2017	80.7
VOBA [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	33.4
Cumulative adjustments for net unrealized investment gains	(79.7)		(81.4)
Amortization of intangibles	13.2	58.9
2014	44.8
2015	39.5
2016	32.2
2017	25.9
DAC [Member]
Finite-Lived Intangible Assets [Line Items]
Cumulative adjustments for net unrealized investment gains	24.9		18.6
Amortization of intangibles	10.0	10.6
Deferred sales inducements, net of shadow adjustments	$ 29.6		$ 26.2
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period	1 year
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period	20 years
Weighted Average [Member] | VOBA [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period	4 years 9 months 18 days