Fair Value - Reconciliations of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, net, Beginning balance	$ 3
Derivative financial instruments, net, Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(1)
Derivative financial instruments, net, Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	0	$ 0
Derivative financial instruments, net, Purchases	0	0
Derivative financial instruments, net, Sales	(2)	3
Derivative financial instruments, net, Settlements	0	0
Derivative financial instruments, net, Transfers into Level 3	0	0
Derivative financial instruments, net, Transfers out of Level 3	0	0
Derivative financial instruments, net, Ending balance		3
Corporate and Other Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	168	162
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	1	(2)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	1	(3)
Purchases	163	65
Sales	(36)	(13)
Settlements	(103)	(35)
Transfers into Level 3		40
Transfers out of Level 3	(64)	(46)
Ending balance	130	168
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		(2)
States, Municipalities and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	2	94
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income		1
Settlements	(1)	(10)
Transfers out of Level 3		(83)
Ending balance	1	2
Residential Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	134	189
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	3	5
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(5)	(3)
Purchases	15	81
Settlements	(14)	(35)
Transfers into Level 3	56	14
Transfers out of Level 3	(60)	(117)
Ending balance	129	134
Commercial Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	22	83
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(1)	7
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(1)	(4)
Purchases	32	23
Settlements	(17)	(17)
Transfers into Level 3	3	17
Transfers out of Level 3	(25)	(87)
Ending balance	13	22
Other Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	53	655
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(2)	3
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	1	3
Purchases	86	130
Sales	(25)	(263)
Settlements	(1)	(52)
Transfers into Level 3	2	7
Transfers out of Level 3	(57)	(430)
Ending balance	57	53
Total Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	209	927
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income		15
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(5)	(4)
Purchases	133	234
Sales	(25)	(263)
Settlements	(32)	(104)
Transfers into Level 3	61	38
Transfers out of Level 3	(142)	(634)
Ending balance	199	209
Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	379	1,183
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	1	14
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(4)	(7)
Purchases	296	299
Sales	(61)	(276)
Settlements	(136)	(149)
Transfers into Level 3	61	78
Transfers out of Level 3	(206)	(763)
Ending balance	330	379
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		(2)
Fixed Maturities Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	85	90
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	5	(3)
Purchases	2
Sales	(86)	(2)
Ending balance	6	85
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	3	(3)
Fixed Maturity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	464	1,273
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	6	11
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(4)	(7)
Purchases	298	299
Sales	(147)	(278)
Settlements	(136)	(149)
Transfers into Level 3	61	78
Transfers out of Level 3	(206)	(763)
Ending balance	336	464
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	3	(5)
Equity Securities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	20	16
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(1)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		(1)
Purchases		4
Transfers into Level 3		1
Ending balance	19	20
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(2)
Equity Securities Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1	1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	1	1
Purchases		1
Sales	(1)	(2)
Ending balance	1	1
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		1
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	21	17
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income		1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		(1)
Purchases		5
Sales	(1)	(2)
Transfers into Level 3		1
Ending balance	20	21
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(2)	1
Life Settlement Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	74	82
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	5	25
Settlements	(21)	(33)
Ending balance	58	74
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	$ (3)	$ 1