Fair Value Measurements - Change in Level 3 Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 6	$ 13	$ 5	$ 25
Total gains or losses (realized/unrealized):
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	5
Purchases	0	0	1	1
Sales	(1)	(1)	(1)	(6)
Transfers into Level 3	0	0	0	1
Transfers out of Level 3	0	0	0	(14)
Ending balance	5	12	5	12
Corporate Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3	4	3	18
Total gains or losses (realized/unrealized):
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	3
Purchases	0	0	0	0
Sales	0	0	0	(4)
Transfers into Level 3	0	0	0	1
Transfers out of Level 3	0	0	0	(14)
Ending balance	3	4	3	4
States, Municipalities And Political Subdivisions Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1	2	1	3
Total gains or losses (realized/unrealized):
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	(1)	(1)	(1)	(2)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Ending balance	0	1	0	1
Preferred Equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	2	7	1	4
Total gains or losses (realized/unrealized):
Included in earnings	0	0	0	0
Included in other comprehensive income	0	0	0	2
Purchases	0	0	1	1
Sales	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Ending balance	$ 2	$ 7	$ 2	$ 7