Fair Value of Financial Instruments - Changes in Fair Value of Financial Instruments (Detail) (USD $)	3 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Document Period End Date	Dec. 31, 2013
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	523,500,000		206,000,000
Total Gains (Losses) Included in Earnings	600,000		(200,000)
Total Gains (Losses) Included in AOCI	(6,700,000)		(2,100,000)
Purchases	192,600,000		134,200,000
Sales			(9,600,000)
Settlements	(500,000)		(700,000)
Net transfer In (Out) of Level 3 (a)		[1]	(14,100,000)	[2]
Balance at End of Period	709,500,000		313,500,000
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	1,875,200,000		1,782,800,000
Total Gains (Losses) Included in Earnings	146,800,000		(102,700,000)
Total Gains (Losses) Included in AOCI	0
Purchases	150,600,000
Sales	0
Settlements	0
Net transfer In (Out) of Level 3	0			[2]
Balance at End of Period	2,172,600,000		1,680,100,000
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	1,544,400,000		1,550,800,000
Total Gains (Losses) Included in Earnings	100,300,000		(33,800,000)
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3		[1]		[2]
Balance at End of Period	1,644,700,000		1,517,000,000
Front Street Future Policyholder Benefits Reserve [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period
Total Gains (Losses) Included in Earnings	(700,000)
Total Gains (Losses) Included in AOCI
Purchases	150,600,000
Sales
Settlements
Net transfer In (Out) of Level 3		[1]
Balance at End of Period	149,900,000
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	330,800,000		232,000,000
Total Gains (Losses) Included in Earnings	47,200,000		(68,900,000)
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3		[1]		[2]
Balance at End of Period	378,000,000		163,100,000
ABS and Hybrids [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net transfer In (Out) of Level 3 (a)			0	[2]
Commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	5,700,000		5,000,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI	300,000		100,000
Purchases			1,000,000
Sales
Settlements	0
Net transfer In (Out) of Level 3 (a)		[1]		[2]
Balance at End of Period	6,000,000		6,100,000
Corporates [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period	461,100,000		135,300,000
Total Gains (Losses) Included in Earnings	0		(200,000)
Total Gains (Losses) Included in AOCI	(6,100,000)		(2,000,000)
Purchases	152,600,000		133,200,000
Sales	0		(9,600,000)
Settlements	(500,000)		(700,000)
Net transfer In (Out) of Level 3 (a)		[1]	100,000	[2]
Balance at End of Period	607,100,000		256,100,000
Hybrids [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period			8,800,000
Total Gains (Losses) Included in Earnings
Total Gains (Losses) Included in AOCI			(100,000)
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3 (a)			(3,700,000)	[2]
Balance at End of Period			5,000,000
Municipals [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at Beginning of Period
Total Gains (Losses) Included in Earnings	0
Total Gains (Losses) Included in AOCI	(700,000)
Purchases	35,000,000
Sales	0
Settlements	0
Net transfer In (Out) of Level 3 (a)		[1]
Balance at End of Period	34,300,000
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	500,000
Total Gains (Losses) Included in AOCI
Purchases
Sales
Settlements
Net transfer In (Out) of Level 3 (a)		[1]		[2]
Balance at End of Period	$ 41,500,000		$ 41,000,000

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjkzMWUzNTc5OTc5ZDQ0NDA5NDZlZDlmNTcyN2JmYzMyfFRleHRTZWxlY3Rpb246REVBMUNFNjUwNzU2Q0U3MUVERDcwNjlDQTlGMzA0OTIM}

[2] (a)The net transfers in and out of Level 3 during the three months ended December 30, 2012 was exclusively to or from Level 2.