Fair Value Measurements - Change in Level 3 Assets (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 53	$ 21	$ 55	$ 20
Total gains or losses (realized/unrealized):
Included in net income	0	1	0	0
Included in other comprehensive income	1	22	0	1
Purchases	0	0	22	22
Sales	(1)	0	(3)	0
Transfers into Level 3	0	0	0	1
Transfers out of Level 3	(11)	(1)	(32)	(1)
Ending balance	42	43	42	43
Corporate Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	52	18	51	18
Total gains or losses (realized/unrealized):
Included in net income	0	1	0	0
Included in other comprehensive income	1	22	1	1
Purchases	0	0	22	22
Sales	(1)	0	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(10)	0	(31)	0
Ending balance	42	41	42	41
Taxable Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1	0	1	0
Total gains or losses (realized/unrealized):
Included in net income	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(1)	0	(1)	0
Ending balance	0	0	0	0
States, Municipalities And Political Subdivisions Fixed Maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	1	0	0
Total gains or losses (realized/unrealized):
Included in net income	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Transfers into Level 3	0	0	0	1
Transfers out of Level 3	0	(1)	0	(1)
Ending balance	0	0	0	0
Preferred Equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	2	3	2
Total gains or losses (realized/unrealized):
Included in net income	0	0	0	0
Included in other comprehensive income	0	0	(1)	0
Purchases	0	0	0	0
Sales	0	0	(2)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Ending balance	$ 0	$ 2	$ 0	$ 2