Goodwill and Intangibles, including DAC and VOBA - Summary of Definite Lived Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified			6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended
	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2013 Minimum [Member]	Mar. 31, 2013 Maximum [Member]	Mar. 31, 2013 Customer relationships [Member]	Sep. 30, 2012 Customer relationships [Member]	Mar. 31, 2013 Customer relationships [Member] Minimum [Member]	Mar. 31, 2013 Customer relationships [Member] Maximum [Member]	Mar. 31, 2013 Trade names [Member]	Sep. 30, 2012 Trade names [Member]	Mar. 31, 2013 Trade names [Member] Minimum [Member]	Mar. 31, 2013 Trade names [Member] Maximum [Member]	Mar. 31, 2013 Technology assets [Member]	Sep. 30, 2012 Technology assets [Member]	Mar. 31, 2013 Technology assets [Member] Minimum [Member]	Mar. 31, 2013 Technology assets [Member] Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	$ 1,209.8	$ 1,038.0			$ 864.6	$ 796.2			$ 170.5	$ 150.8			$ 174.7	$ 91.0
Accumulated Amortization	203.7	164.1			136.5	113.0			36.9	28.3			30.3	22.8
Net	$ 1,006.1	$ 873.9			$ 728.1	$ 683.2			$ 133.6	$ 122.5			$ 144.4	$ 68.2
Amortizable Life			1 year	20 years			15 years	20 years			1 year	12 years			4 years	17 years