Fair Value of Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended				9 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers Between Asset Classification	$ 6,000,000				$ 6,000,000
Percentage of male contractholder					50.00%
Percentage of female contractholder					50.00%
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0		79,300,000		0		79,300,000
Net transfer In (Out) of Level 3 (a)	(18,900,000)	[1],[2]		[2]	(23,900,000)	[1],[2]	(53,000,000)	[2]
Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net transfer In (Out) of Level 3 (a)	$ (4,800,000)	[1]		[2]	$ (3,800,000)	[1]	$ (10,500,000)	[2]

[1] This includes a $6.0 transfer to asset-backed securities from commercial mortgage-backed securities, the remaining transfers were from level 3 to level 2.

[2] (a)The net transfers in and out of Level 3 during the nine months ended June 30, 2013 were exclusively to or from Level 2.