Summary of Changes in Fair Value Associated With Level 3 Assets (Parenthetical) (Detail) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011		Jun. 30, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transferred out of Level 3 into Level 2	$ 0	$ 0	$ (15.4)	[1]	$ (41.0)	[2]
Redeemable Preferred Stock | Industrial, Miscellaneous, and All Others | Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transferred out of Level 3 into Level 2	0	0	0	[1]	(53.1)	[2]
Transferred out of Level 3 into Level 2					(53.1)
Residential Mortgage Backed Securities | Asset-backed Securities | Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transferred out of Level 3 into Level 2	0	0	(15.4)	[1]	12.1	[2]
Transferred out of Level 2 into Level 3					12.1
Asset-backed Securities | Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transferred out of Level 3 into Level 2	0	0	(15.4)	[1]	12.1	[2]
Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transferred out of Level 3 into Level 2	$ 0	$ 0	$ (15.4)	[1]	$ (41.0)	[2]

[1] The $(15.4) million was transferred out of Level 3 into Level 2 due to the availability of vendor pricing on a residential mortgage-backed security.

[2] The $12.1 million was transferred from Level 2 into Level 3 due to a lack of trade volume and the $(53.1) million was transferred out of Level 3 into Level 2 due to the availability of vendor pricing on a redeemable preferred stock.