Change in Level 3 Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 25	$ 21	$ 25	$ 31
Total gains or losses (realized/unrealized):
Included in earnings
Included in other comprehensive income		1	5	1
Purchases		7	1	7
Sales	(1)		(5)
Transfers into Level 3			1	1
Transfers out of Level 3	(11)	(3)	(14)	(14)
Ending balance	13	26	13	26
Corporate Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	16	11	18	20
Total gains or losses (realized/unrealized):
Included in earnings
Included in other comprehensive income			3
Purchases		7		7
Sales	(1)		(4)
Transfers into Level 3			1
Transfers out of Level 3	(11)	(3)	(14)	(12)
Ending balance	4	15	4	15
US States and Political Subdivisions Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	2	4	3	4
Total gains or losses (realized/unrealized):
Included in earnings
Sales			(1)
Ending balance	2	4	2	4
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	7	6	4	5
Total gains or losses (realized/unrealized):
Included in earnings
Included in other comprehensive income		1	2	1
Purchases			1
Transfers into Level 3				1
Ending balance	7	7	7	7
Taxable Fixed Maturities | Separate Accounts Asset
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance				2
Total gains or losses (realized/unrealized):
Included in earnings
Transfers out of Level 3				$ (2)