Fair Value - Reconciliations of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 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 (Loss)	$ (2)		(3)
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)
Derivative financial instruments, net, Settlements	0		0
Derivative financial instruments, net, Transfers into Level 3	3		3
Derivative financial instruments, net, Transfers out of Level 3	0		0
Derivative financial instruments, net, Ending balance	1		1
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30	(3)		(3)
Corporate and Other Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	193	$ 186	168	$ 162
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	1	(2)		(1)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	3	(1)	7	(1)
Purchases	94		147	12
Sales	(20)		(36)	(12)
Settlements	(7)	(7)	(10)	(21)
Transfers into Level 3				37
Transfers out of Level 3	(22)	(35)	(34)	(35)
Ending balance	242	141	242	141
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30		(3)		(3)
States, Municipalities and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	2	86	2	94
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)				1
Settlements		(1)		(10)
Ending balance	2	85	2	85
Residential Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	128	232	134	189
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	1	1	2	2
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(1)	(2)	(1)	(2)
Purchases	10		10	72
Settlements	(4)	(11)	(9)	(21)
Transfers out of Level 3		(13)	(2)	(33)
Ending balance	134	207	134	207
Commercial Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	27	64	22	83
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)		1		2
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		(1)
Purchases		9	9	15
Settlements	(9)	(1)	(9)	(2)
Transfers into Level 3	3	17	3	17
Transfers out of Level 3	(10)	(2)	(14)	(28)
Ending balance	11	87	11	87
Other Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	50	553	53	655
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)		2		3
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	2	1	2	10
Purchases	35	47	35	82
Sales	(25)	(90)	(25)	(234)
Settlements	(1)	(17)	(1)	(20)
Transfers into Level 3			2
Transfers out of Level 3	(16)	(6)	(21)	(6)
Ending balance	45	490	45	490
Total Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	205	849	209	927
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	1	4	2	7
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	1	(2)	1	8
Purchases	45	56	54	169
Sales	(25)	(90)	(25)	(234)
Settlements	(14)	(29)	(19)	(43)
Transfers into Level 3	3	17	5	17
Transfers out of Level 3	(26)	(21)	(37)	(67)
Ending balance	190	784	190	784
Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	400	1,121	379	1,183
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	2	2	2	7
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	4	(3)	8	7
Purchases	139	56	201	181
Sales	(45)	(90)	(61)	(246)
Settlements	(21)	(37)	(29)	(74)
Transfers into Level 3	3	17	5	54
Transfers out of Level 3	(48)	(56)	(71)	(102)
Ending balance	434	1,010	434	1,010
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30		(3)		(3)
Fixed Maturities Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	3	89	85	90
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	4		5
Purchases			2
Sales	(1)		(86)	(1)
Ending balance	6	89	6	89
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30	4		4
Fixed Maturity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	403	1,210	464	1,273
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	6	2	7	7
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	4	(3)	8	7
Purchases	139	56	203	181
Sales	(46)	(90)	(147)	(247)
Settlements	(21)	(37)	(29)	(74)
Transfers into Level 3	3	17	5	54
Transfers out of Level 3	(48)	(56)	(71)	(102)
Ending balance	440	1,099	440	1,099
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30	4	(3)	4	(3)
Equity Securities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	19	13	20	16
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		3	(1)
Ending balance	19	16	19	16
Equity Securities Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		1	1	1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	1		1
Purchases	1		1
Sales			(1)
Ending balance	2	1	2	1
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30	1		1
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	19	14	21	17
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	1		1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		3	(1)
Purchases	1		1
Sales			(1)
Ending balance	21	17	21	17
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30	1		1
Life Settlement Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	72	79	74	82
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income (Loss)	6	4	10	17
Settlements	(11)	(8)	(17)	(24)
Ending balance	67	75	67	75
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30	$ (3)	$ (2)	$ (3)	$ (1)