Fair Value - Reconciliations of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Derivative Financial Instruments, Net [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (3)	$ 5
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	1	8
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		(9)
Purchases		(2)
Sales	2	1
Settlements		(6)
Ending balance		(3)
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	2	1
Corporate and Other Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	204	219
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)
Purchases	33	123
Sales	(23)	(97)
Settlements	(16)	(44)
Transfers into Level 3	18	51
Transfers out of Level 3	(55)	(51)
Ending balance	162	204
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	71	96
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	4	4
Purchases	14	122
Sales	(10)	(79)
Settlements		(61)
Transfers into Level 3	14	18
Transfers out of Level 3		(27)
Ending balance	94	71
Residential Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	331	413
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(21)	4
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	61	(14)
Purchases	94	116
Sales	(174)	(10)
Settlements	(72)	(75)
Transfers into Level 3	32	4
Transfers out of Level 3	(62)	(107)
Ending balance	189	331
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		(3)
Commercial Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	151	129
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	7
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(6)	11
Purchases	28	107
Sales	(60)	(3)
Settlements	(29)	(11)
Transfers into Level 3	43	21
Transfers out of Level 3	(51)	(103)
Ending balance	83	151
Other Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	446	368
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	2	5
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(6)	(4)
Purchases	488	314
Sales	(111)	(197)
Settlements	(117)	(35)
Transfers out of Level 3	(47)	(5)
Ending balance	655	446
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(1)	(2)
Total Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	928	910
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(12)	9
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	49	(7)
Purchases	610	537
Sales	(345)	(210)
Settlements	(218)	(121)
Transfers into Level 3	75	25
Transfers out of Level 3	(160)	(215)
Ending balance	927	928
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(1)	(5)
Redeemable Preferred Stock [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		26
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income		(1)
Settlements		(25)
Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1,203	1,251
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(9)	9
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	52	(3)
Purchases	657	782
Sales	(378)	(386)
Settlements	(234)	(251)
Transfers into Level 3	107	94
Transfers out of Level 3	(215)	(293)
Ending balance	1,183	1,203
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	(1)	(7)
Fixed Maturities, Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	80	89
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	11	(4)
Purchases		19
Sales	(1)	(24)
Ending balance	90	80
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	11	(4)
Fixed Maturity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1,283	1,340
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	2	5
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	52	(3)
Purchases	657	801
Sales	(379)	(410)
Settlements	(234)	(251)
Transfers into Level 3	107	94
Transfers out of Level 3	(215)	(293)
Ending balance	1,273	1,283
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	10	(11)
Total Equity Securities Available-for-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	11	34
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	3	(27)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(6)	3
Purchases	16	2
Sales	(8)
Transfers out of Level 3		(1)
Ending balance	16	11
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31		(27)
Equity Securities, Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	8	7
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	(1)	(5)
Purchases		6
Sales	(6)
Ending balance	1	8
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	1	(5)
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	19	41
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	2	(32)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(6)	3
Purchases	16	8
Sales	(14)
Transfers out of Level 3		(1)
Ending balance	17	19
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	1	(32)
Short Term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		6
Sales		(6)
Other Invested Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		1
Sales		(1)
Life Settlement Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	88	100
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	33	13
Settlements	(39)	(25)
Ending balance	82	88
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at December 31	8	(2)
Separate Account Business [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1	2
Purchases		1
Sales		(2)
Transfers out of Level 3	(1)
Ending balance		$ 1

Unrealized gains (losses) Recognized in Net Income on Level 3 Assets and Liabilities Held

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

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Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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