Fair Value (Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Corporate And Other Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 488	$ 812	$ 482	$ 624
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	1	(7)	7	(5)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	(4)	(3)	2	(6)
Purchases	50	113	196	459
Sales	(5)	(107)	(117)	(157)
Settlements	(11)	(47)	(43)	(144)
Transfers into Level 3		12	42	52
Transfers out of Level 3	(260)	(154)	(310)	(204)
Ending balance	259	619	259	619
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	(1)	(10)	(1)	(11)
States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	89	179	171	266
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI			3
Purchases		3		3
Settlements			(85)	(87)
Transfers out of Level 3
Ending balance	89	182	89	182
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	443	687	452	767
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	(17)	1	(15)	(11)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	20	(5)	(2)	9
Purchases	21	73	81	170
Sales		(81)		(164)
Settlements	(8)	(13)	(24)	(54)
Transfers out of Level 3	(22)	(31)	(55)	(86)
Ending balance	437	631	437	631
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	(18)		(18)	(15)
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	166	95	59	73
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	4		6	3
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	6	(7)	14	11
Purchases	12	76	141	81
Sales			(12)	(4)
Settlements	(17)		(21)
Transfers into Level 3	11		11
Transfers out of Level 3	(65)	(5)	(81)	(5)
Ending balance	117	159	117	159
Other Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	434	491	343	359
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	2	(5)	8
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	5	(6)	8	(6)
Purchases	143	114	501	441
Sales	(117)	(105)	(293)	(236)
Settlements	(34)	(25)	(93)	(80)
Transfers into Level 3		2		2
Transfers out of Level 3	(62)	(37)	(103)	(51)
Ending balance	371	429	371	429
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30		(4)		(4)
Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1,043	1,273	854	1,199
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	(11)	(4)	(1)	(8)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	31	(18)	20	14
Purchases	176	263	723	692
Sales	(117)	(186)	(305)	(404)
Settlements	(59)	(38)	(138)	(134)
Transfers into Level 3	11	2	11	2
Transfers out of Level 3	(149)	(73)	(239)	(142)
Ending balance	925	1,219	925	1,219
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	(18)	(4)	(18)	(19)
Fixed Maturities Available-For-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1,647	2,264	1,507	2,092
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	(10)	(11)	6	(10)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	26	(21)	24	5
Purchases	226	379	972	1,154
Sales	(122)	(293)	(448)	(564)
Settlements	(70)	(85)	(266)	(365)
Transfers into Level 3	11	14	53	54
Transfers out of Level 3	(409)	(227)	(549)	(346)
Ending balance	1,299	2,020	1,299	2,020
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	(19)	(14)	(19)	(30)
Fixed Maturities, Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	94	114	101	184
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income		(3)	(7)	(1)
Purchases			1
Sales	(1)		(2)	(72)
Ending balance	93	111	93	111
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30		(3)	(7)	6
Fixed Maturity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	1,741	2,378	1,608	2,276
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	(10)	(14)	(1)	(11)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	26	(21)	24	5
Purchases	226	379	973	1,154
Sales	(123)	(293)	(450)	(636)
Settlements	(70)	(85)	(266)	(365)
Transfers into Level 3	11	14	53	54
Transfers out of Level 3	(409)	(227)	(549)	(346)
Ending balance	1,392	2,131	1,392	2,131
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	(19)	(17)	(26)	(24)
Equity Securities Available-For-Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	93	36	67	26
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	(19)		(19)	(2)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	(10)		6	(1)
Purchases			26	19
Sales		(1)	(16)	(12)
Transfers into Level 3				5
Transfers out of Level 3	(14)	(3)	(14)	(3)
Ending balance	50	32	50	32
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	(19)		(21)	(3)
Equity Securities, Trading [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	9	16	14	6
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	2	(4)	(3)	(9)
Purchases				1
Transfers into Level 3				14
Ending balance	11	12	11	12
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	3	(4)	(1)	(9)
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	102	52	81	32
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	(17)	(4)	(22)	(11)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	(10)		6	(1)
Purchases			26	20
Sales		(1)	(16)	(12)
Transfers into Level 3				19
Transfers out of Level 3	(14)	(3)	(14)	(3)
Ending balance	61	44	61	44
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	(16)	(4)	(22)	(12)
Short Term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	4	6	27	27
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income
Purchases	7		23	12
Sales	(4)		(4)
Settlements			(39)	(23)
Transfers into Level 3	1		1
Transfers out of Level 3				(10)
Ending balance	8	6	8	6
Other Invested Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	11	10	11	26
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income				3
Sales				(19)
Transfers out of Level 3
Ending balance	11	10	11	10
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30				1
Life Settlement Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	116	129	117	129
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	7	11	30	20
Settlements	(10)	(15)	(34)	(24)
Ending balance	113	125	113	125
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30		(1)	3	2
Separate Account Business [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	3	37	23	41
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income
Sales		(2)	(20)	(6)
Transfers out of Level 3
Ending balance	3	35	3	35
Redeemable Preferred Stock [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	27			3
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)		(1)	(3)
Purchases			53
Sales			(26)	(3)
Ending balance	26		26
Derivative Financial Instruments, Net [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	12	(37)	(15)	(21)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in Net Income	(1)	(13)	(5)	(32)
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses) Included in OCI	(5)	11	29	(5)
Purchases
Sales			(6)
Settlements	(1)	11	2	30
Transfers into Level 3
Transfers out of Level
Ending balance	5	(28)	5	(28)
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	$ (2)	$ (1)	$ (1)	$ (1)