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
	Mar. 31, 2016	Mar. 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
Derivative financial instruments, net, Purchases	0
Derivative financial instruments, net, Sales	(2)
Derivative financial instruments, net, Settlements	0
Derivative financial instruments, net, Transfers into Level 3	0
Derivative financial instruments, net, Transfers out of Level 3	0
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)	1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	4
Purchases	53	12
Sales	(16)	(12)
Settlements	(3)	(14)
Transfers into Level 3		37
Transfers out of Level 3	(12)
Ending balance	193	186
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		(9)
Ending balance	2	86
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	1	1
Purchases		72
Settlements	(5)	(10)
Transfers out of Level 3	(2)	(20)
Ending balance	128	232
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
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		1
Purchases	9	6
Settlements		(1)
Transfers out of Level 3	(4)	(26)
Ending balance	27	64
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		1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		9
Purchases		35
Sales		(144)
Settlements		(3)
Transfers into Level 3	2
Transfers out of Level 3	(5)
Ending balance	50	553
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	1	3
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		10
Purchases	9	113
Sales		(144)
Settlements	(5)	(14)
Transfers into Level 3	2
Transfers out of Level 3	(11)	(46)
Ending balance	205	849
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		5
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	4	10
Purchases	62	125
Sales	(16)	(156)
Settlements	(8)	(37)
Transfers into Level 3	2	37
Transfers out of Level 3	(23)	(46)
Ending balance	400	1,121
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	1
Purchases	2
Sales	(85)	(1)
Ending balance	3	89
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	1	5
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	4	10
Purchases	64	125
Sales	(101)	(157)
Settlements	(8)	(37)
Transfers into Level 3	2	37
Transfers out of Level 3	(23)	(46)
Ending balance	403	1,210
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 OCI	(1)	(3)
Ending balance	19	13
Equity Securities Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1	1
Sales	(1)
Ending balance		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 OCI	(1)	(3)
Sales	(1)
Ending balance	19	14
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	4	13
Settlements	(6)	(16)
Ending balance	72	79
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at March 31	$ 1	$ 1