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, 2015	Dec. 31, 2014
Derivative Financial Instruments, Net [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		$ (3)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income		1
Sales	$ 3	2
Ending balance	3
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		2
Corporate and Other Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	162	204
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(2)	2
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(3)	(1)
Purchases	65	33
Sales	(13)	(23)
Settlements	(35)	(16)
Transfers into Level 3	40	18
Transfers out of Level 3	(46)	(55)
Ending balance	168	162
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	94	71
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	1	1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		4
Purchases		14
Sales		(10)
Settlements	(10)
Transfers into Level 3		14
Transfers out of Level 3	(83)
Ending balance	2	94
Residential Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	189	331
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	5	(21)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(3)	61
Purchases	81	94
Sales		(174)
Settlements	(35)	(72)
Transfers into Level 3	14	32
Transfers out of Level 3	(117)	(62)
Ending balance	134	189
Commercial Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	83	151
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	7	7
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(4)	(6)
Purchases	23	28
Sales		(60)
Settlements	(17)	(29)
Transfers into Level 3	17	43
Transfers out of Level 3	(87)	(51)
Ending balance	22	83
Other Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	655	446
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	3	2
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	3	(6)
Purchases	130	488
Sales	(263)	(111)
Settlements	(52)	(117)
Transfers into Level 3	7
Transfers out of Level 3	(430)	(47)
Ending balance	53	655
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		(1)
Total Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	927	928
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	15	(12)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(4)	49
Purchases	234	610
Sales	(263)	(345)
Settlements	(104)	(218)
Transfers into Level 3	38	75
Transfers out of Level 3	(634)	(160)
Ending balance	209	927
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		(1)
Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1,183	1,203
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	14	(9)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(7)	52
Purchases	299	657
Sales	(276)	(378)
Settlements	(149)	(234)
Transfers into Level 3	78	107
Transfers out of Level 3	(763)	(215)
Ending balance	379	1,183
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(2)	(1)
Fixed Maturities Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	90	80
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(3)	11
Sales	(2)	(1)
Ending balance	85	90
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(3)	11
Fixed Maturity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1,273	1,283
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	11	2
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(7)	52
Purchases	299	657
Sales	(278)	(379)
Settlements	(149)	(234)
Transfers into Level 3	78	107
Transfers out of Level 3	(763)	(215)
Ending balance	464	1,273
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(5)	10
Total Equity Securities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	16	11
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income		3
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(1)	(6)
Purchases	4	16
Sales		(8)
Transfers into Level 3	1
Ending balance	20	16
Equity Securities Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1	8
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	1	(1)
Purchases	1
Sales	(2)	(6)
Ending balance	1	1
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	1	1
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	17	19
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)	(6)
Purchases	5	16
Sales	(2)	(14)
Transfers into Level 3	1
Ending balance	21	17
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	1	1
Life Settlement Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	82	88
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	25	33
Settlements	(33)	(39)
Ending balance	74	82
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	$ 1	8
Separate Account Business [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		1
Transfers out of Level 3		$ (1)