Fair Value of Financial Instruments - Changes in Fair Value of Financial Instruments (Detail) (USD $)	3 Months Ended				6 Months Ended
	Mar. 31, 2013		Apr. 01, 2012		Mar. 31, 2013		Apr. 01, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount			$ 0				$ 0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	313,500,000		551,400,000		206,000,000		546,500,000
Total Gains (Losses) Included in Earnings	(100,000)		41,100,000		(300,000)		41,000,000
Total Gains (Losses) Included in AOCI	3,300,000		9,300,000		1,200,000		3,700,000
Purchases	154,200,000		105,100,000		288,400,000		143,900,000
Sales			(9,700,000)		(9,600,000)		(16,700,000)
Settlements	(13,000,000)		(21,700,000)		(13,700,000)		(32,600,000)
Net transfer In (Out) of Level 3 (a)	(38,900,000)	[1]	8,600,000	[2]	(53,000,000)	[1]	(1,700,000)	[2]
Balance at End of Period	419,000,000		684,100,000		419,000,000		684,100,000
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	1,680,100,000		1,502,900,000		1,782,800,000		1,472,100,000
Total Gains (Losses) Included in Earnings	162,200,000		68,100,000		59,500,000		98,900,000
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3		[1]		[2]		[1]		[2]
Balance at End of Period	1,842,300,000		1,571,000,000		1,842,300,000		1,571,000,000
FIA embedded derivatives, included in contractholder funds [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	1,517,000,000		1,455,000,000		1,550,800,000		1,396,300,000
Total Gains (Losses) Included in Earnings	122,600,000		41,700,000		88,800,000		100,400,000
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3		[1]		[2]		[1]		[2]
Balance at End of Period	1,639,600,000		1,496,700,000		1,639,600,000		1,496,700,000
Equity conversion feature of preferred stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	163,100,000		47,500,000		232,000,000		75,400,000
Total Gains (Losses) Included in Earnings	39,600,000		26,400,000		(29,300,000)		(1,500,000)
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3		[1]		[2]		[1]		[2]
Balance at End of Period	202,700,000		73,900,000		202,700,000		73,900,000
Available-for-sale embedded derivatives [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period			400,000				400,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3				[2]				[2]
Balance at End of Period			400,000				400,000
US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	79,300,000				79,300,000
Asset-backed and Hybrid Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	38,900,000				53,000,000
Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	5,300,000		400,700,000		15,900,000		374,500,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI			10,700,000		(100,000)		6,100,000
Purchases			93,600,000				132,400,000
Sales
Settlements			(12,800,000)				(20,800,000)
Net transfer In (Out) of Level 3 (a)		[1]	10,800,000	[2]	(10,500,000)	[1]	10,800,000	[2]
Balance at End of Period	5,300,000		503,000,000		5,300,000		503,000,000
Commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	6,100,000				5,000,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI	100,000				200,000
Purchases					1,000,000
Sales
Settlements
Net transfer In (Out) of Level 3 (a)		[1]				[1]
Balance at End of Period	6,200,000				6,200,000
Corporates [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	256,100,000		138,500,000		135,300,000		159,700,000
Total Gains (Losses) Included in Earnings	(100,000)		100,000		(300,000)
Total Gains (Losses) Included in AOCI	3,200,000		(1,400,000)		1,200,000		(2,300,000)
Purchases	144,200,000		1,300,000		277,400,000		1,300,000
Sales			(9,700,000)		(9,600,000)		(16,700,000)
Settlements	(13,000,000)		(8,800,000)		(13,700,000)		(11,600,000)
Net transfer In (Out) of Level 3 (a)	(33,900,000)	[1]	100,000	[2]	(33,800,000)	[1]	(10,300,000)	[2]
Balance at End of Period	356,500,000		120,100,000		356,500,000		120,100,000
Hybrids [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	5,000,000		5,100,000		8,800,000		5,200,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI					(100,000)		(100,000)
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3 (a)	(5,000,000)	[1]		[2]	(8,700,000)	[1]		[2]
Balance at End of Period			5,100,000				5,100,000
Municipals [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period			100,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI			100,000				100,000
Purchases			10,200,000				10,200,000
Sales
Settlements
Net transfer In (Out) of Level 3 (a)				[2]			100,000	[2]
Balance at End of Period			10,400,000				10,400,000
Agency residential mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period			3,300,000				3,300,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3 (a)				[2]				[2]
Balance at End of Period			3,300,000				3,300,000
Non-agency residential mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period			3,700,000				3,800,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI			(100,000)				(100,000)
Purchases
Sales
Settlements			(100,000)				(200,000)
Net transfer In (Out) of Level 3 (a)			(2,300,000)	[2]			(2,300,000)	[2]
Balance at End of Period			1,200,000				1,200,000
Equity securities available-for-sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	0				0
Total Gains (Losses) Included in Earnings	0				0
Total Gains (Losses) Included in AOCI	0				0
Purchases	10,000,000				10,000,000
Sales	0				0
Settlements	0				0
Net transfer In (Out) of Level 3 (a)	0				0
Balance at End of Period	10,000,000				10,000,000
Corporate and Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			2,300,000				12,600,000
Contingent purchase price reduction receivable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	41,000,000				41,000,000
Total Gains (Losses) Included in Earnings			41,000,000				41,000,000
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3 (a)		[1]		[2]		[1]		[2]
Balance at End of Period	$ 41,000,000		$ 41,000,000		$ 41,000,000		$ 41,000,000

[1] The net transfers in and out of Level 3 during the three and six months ended March 31, 2013 were exclusively to or from Level 2.

[2] The net transfers in and out of Level 3 during the three and six months ended April 1, 2012 was exclusively to or from Level 2.