Fair Value - Reconciliation of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended					6 Months Ended
	Jun. 30, 2013	Jun. 30, 2014 Derivative Financial Instruments, Net [Member]	Jun. 30, 2013 Derivative Financial Instruments, Net [Member]	Jun. 30, 2014 Derivative Financial Instruments, Net [Member]	Jun. 30, 2013 Derivative Financial Instruments, Net [Member]	Jun. 30, 2014 Corporate and Other Bonds [Member]	Jun. 30, 2013 Corporate and Other Bonds [Member]	Jun. 30, 2014 Corporate and Other Bonds [Member]	Jun. 30, 2013 Corporate and Other Bonds [Member]	Jun. 30, 2014 States, Municipalities and Political Subdivisions [Member]	Jun. 30, 2013 States, Municipalities and Political Subdivisions [Member]	Jun. 30, 2014 States, Municipalities and Political Subdivisions [Member]	Jun. 30, 2013 States, Municipalities and Political Subdivisions [Member]	Jun. 30, 2014 Residential Mortgage-Backed [Member]	Jun. 30, 2013 Residential Mortgage-Backed [Member]	Jun. 30, 2014 Residential Mortgage-Backed [Member]	Jun. 30, 2013 Residential Mortgage-Backed [Member]	Jun. 30, 2014 Commercial Mortgage-Backed [Member]	Jun. 30, 2013 Commercial Mortgage-Backed [Member]	Jun. 30, 2014 Commercial Mortgage-Backed [Member]	Jun. 30, 2013 Commercial Mortgage-Backed [Member]	Jun. 30, 2014 Other Asset-Backed [Member]	Jun. 30, 2013 Other Asset-Backed [Member]	Jun. 30, 2014 Other Asset-Backed [Member]	Jun. 30, 2013 Other Asset-Backed [Member]	Jun. 30, 2014 Total Asset-Backed [Member]	Jun. 30, 2013 Total Asset-Backed [Member]	Jun. 30, 2014 Total Asset-Backed [Member]	Jun. 30, 2013 Total Asset-Backed [Member]	Jun. 30, 2014 Total Fixed Maturities Available-for-Sale [Member]	Jun. 30, 2013 Total Fixed Maturities Available-for-Sale [Member]	Jun. 30, 2014 Total Fixed Maturities Available-for-Sale [Member]	Jun. 30, 2013 Total Fixed Maturities Available-for-Sale [Member]	Jun. 30, 2014 Fixed Maturities, Trading [Member]	Jun. 30, 2013 Fixed Maturities, Trading [Member]	Jun. 30, 2014 Fixed Maturities, Trading [Member]	Jun. 30, 2013 Fixed Maturities, Trading [Member]	Jun. 30, 2014 Fixed Maturity Securities [Member]	Jun. 30, 2013 Fixed Maturity Securities [Member]	Jun. 30, 2014 Fixed Maturity Securities [Member]	Jun. 30, 2013 Fixed Maturity Securities [Member]	Jun. 30, 2013 Total Equity Securities Available-for-Sale [Member]	Jun. 30, 2014 Total Equity Securities Available-for-Sale [Member]	Jun. 30, 2013 Total Equity Securities Available-for-Sale [Member]	Mar. 31, 2014 Total Equity Securities Available-for-Sale [Member]	Jun. 30, 2014 Equity Securities, Trading [Member]	Jun. 30, 2013 Equity Securities, Trading [Member]	Jun. 30, 2014 Equity Securities, Trading [Member]	Jun. 30, 2013 Equity Securities, Trading [Member]	Jun. 30, 2014 Equity Securities [Member]	Jun. 30, 2013 Equity Securities [Member]	Jun. 30, 2014 Equity Securities [Member]	Jun. 30, 2013 Equity Securities [Member]	Jun. 30, 2014 Life Settlement Contracts [Member]	Jun. 30, 2013 Life Settlement Contracts [Member]	Jun. 30, 2014 Life Settlement Contracts [Member]	Jun. 30, 2013 Life Settlement Contracts [Member]	Jun. 30, 2013 Redeemable Preferred Stock [Member]	Jun. 30, 2013 Redeemable Preferred Stock [Member]	Jun. 30, 2013 Short Term Investments [Member]	Jun. 30, 2013 Short Term Investments [Member]	Jun. 30, 2014 Separate Account Business [Member]	Jun. 30, 2013 Separate Account Business [Member]	Mar. 31, 2013 Separate Account Business [Member]	Dec. 31, 2012 Separate Account Business [Member]	Jun. 30, 2013 Other Invested Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 5	$ (4)	$ 2	$ (3)	$ 5	$ 189	$ 283	$ 204	$ 219	$ 86	$ 129	$ 71	$ 96	$ 359	$ 450	$ 331	$ 413	$ 126	$ 177	$ 151	$ 129	$ 439	$ 396	$ 446	$ 368	$ 924	$ 1,023	$ 928	$ 910	$ 1,199	$ 1,461	$ 1,203	$ 1,251	$ 85	$ 107	$ 80	$ 89	$ 1,284	$ 1,568	$ 1,283	$ 1,340	$ 19	$ 11	$ 34	$ 2	$ 2	$ 3	$ 8	$ 7	$ 4	$ 22	$ 19	$ 41	$ 87	$ 95	$ 88	$ 100	$ 26	$ 26	$ 5	$ 6	$ 1	$ 2	$ 2	$ 2	$ 1
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income	5	1	2	1	5	1	1	2	1	1		1	(3)	(24)	(1)	(23)	2	1		2	1			1	3	(23)	(1)	(20)	6	(21)		(17)	4	6		11	1	(15)		(6)	5	(5)	3	(20)		1	(1)		(5)	1	(6)	3	(25)	12	4	22	11
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI	(2)		2		(2)		(3)	1	(1)	1	4	2	4	47	(1)	62	(1)	1	4		9	4	(3)	4	(2)	52		66	6	53		69	8					53		69	8	(1)	(4)								(1)	(4)						(1)	(1)
Purchases	1		1	(2)	1	21	13	26	104	1	37	1	122	22	50	47	111		5		78	229	38	377	174	251	93	424	363	273	143	451	589				19	273	143	451	608					1		2		1		2
Sales		1	(1)	2		(6)	(54)	(10)	(71)	(10)	(32)	(10)	(79)	(174)	(10)	(174)	(10)	(60)		(60)		(28)	(33)	(111)	(132)	(262)	(43)	(345)	(142)	(278)	(129)	(365)	(292)		(20)		(22)	(278)	(149)	(365)	(314)		(8)					(6)				(14)								(5)	(6)					(1)
Settlements	(4)		(1)		(4)	(5)	(6)	(10)	(26)		(3)		(5)	(19)	(21)	(40)	(32)	(1)	(2)	(2)	(9)	(18)	(11)	(90)	(24)	(38)	(34)	(132)	(65)	(43)	(43)	(142)	(96)					(43)	(43)	(142)	(96)													(13)	(8)	(24)	(20)
Transfers into Level 3						5		8	26		5	14	5		4	21	4	12	21	12	21					12	25	33	25	17	30	55	56					17	30	55	56
Transfers out of Level 3		2		2		(11)	(32)	(27)	(50)					(26)	(43)	(39)	(59)	(20)	(40)	(44)	(64)			(1)		(46)	(83)	(84)	(123)	(57)	(115)	(111)	(173)					(57)	(115)	(111)	(173)			(1)									(1)									(1)
Ending balance	5		5		5	194	202	194	202	79	140	79	140	185	428	185	428	59	165	59	165	626	387	626	387	870	980	870	980	1,143	1,347	1,143	1,347	91	87	91	87	1,234	1,434	1,234	1,434	13	2	13	2	4	2	4	2	6	15	6	15	86	91	86	91	25	25				2	2	2
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at June 30	$ 1			$ 2	$ 1		$ (1)		$ (2)						$ (2)		$ (2)					$ (1)	$ (1)	$ (1)	$ (1)	$ (1)	$ (3)	$ (1)	$ (3)	$ (1)	$ (4)	$ (1)	$ (5)	$ 6		$ 11	$ 1	$ 5	$ (4)	$ 10	$ (4)	$ (5)		$ (20)		$ 1	$ (2)		$ (5)	$ 1	$ (7)		$ (25)	$ 1	$ (1)	$ 2	$ 1