Goodwill and Intangibles, including DAC and VOBA - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Sep. 30, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill, Acquired During Period			$ 65.2
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	77.5		77.5
Intangible assets amortization method			straight-line method
Amortization of intangibles	40.7	85.0	121.5	220.6
2014	80.7		80.7
2015	80.7		80.7
2016	80.7		80.7
2017	80.7		80.7
VOBA [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	7.9		7.9
Cumulative adjustments for net unrealized investment gains	(189.7)		(189.7)		(81.4)
Amortization of intangibles	10.8	37.3	34.9	113.0
2014	42.1		42.1
2015	38.4		38.4
2016	31.7		31.7
2017	25.8		25.8
DAC [Member]
Finite-Lived Intangible Assets [Line Items]
Cumulative adjustments for net unrealized investment gains	(64.4)		(64.4)		18.6
Amortization of intangibles	9.4	27.4	25.4	50.1
Deferred sales inducements, net of shadow adjustments	29.8		29.8		26.2
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			1 year
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			20 years
Weighted Average [Member] | VOBA [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life			5 years 0 months 0 days
Hardware Acquisition [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill, Acquired During Period			$ 3.5