Fair Value Measurements - Change in Level 3 Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 20	$ 4
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers into Level 3	1	11
Transfers out of Level 3	0	0
Ending balance	21	15
Corporate Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	18	2
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers into Level 3	0	6
Transfers out of Level 3	0	0
Ending balance	18	8
Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	0
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers into Level 3	0	5
Transfers out of Level 3	0	0
Ending balance	0	5
States, Municipalities And Political Subdivisions Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	0
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers into Level 3	1	0
Transfers out of Level 3	0	0
Ending balance	1	0
Preferred Equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	2	2
Total gains or losses (realized/unrealized):
Included in net income	0	0
Included in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Ending balance	$ 2	$ 2