Goodwill and Intangibles, including DAC and VOBA - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended		15 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Jul. 01, 2012	Jul. 01, 2013	Sep. 30, 2012
Finite-Lived Intangible Assets [Line Items]
Intangible assets amortization method		straight-line method
Amortization of intangibles	$ 85.0	$ 220.6	$ 158.5	$ 43.0
2014	78.5	78.5
2015	78.5	78.5
2016	78.5	78.5
2017	78.5	78.5
VOBA [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period		4 years 10 months 24 days
Cumulative adjustments for net unrealized investment gains	128.1	128.1			339.4
Amortization of intangibles	37.3	113.0	101.3	23.8
2014	45.7	45.7
2015	43.7	43.7
2016	39.5	39.5
2017	33.0	33.0
DAC [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period		7 years 8 months 12 days
Cumulative adjustments for net unrealized investment gains	1.1	1.1			50.7
Amortization of intangibles	27.4	50.1	10.7	3.1
Deferred sales inducements, net of shadow adjustments	20.6	20.6			9.1
2014	22.3	22.3
2015	23.6	23.6
2016	22.9	22.9
2017	$ 22.0	$ 22.0
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