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	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended
	Sep. 30, 2014 Derivative Financial Instruments, Net [Member]	Sep. 30, 2013 Derivative Financial Instruments, Net [Member]	Sep. 30, 2014 Derivative Financial Instruments, Net [Member]	Sep. 30, 2013 Derivative Financial Instruments, Net [Member]	Sep. 30, 2014 Corporate and Other Bonds [Member]	Sep. 30, 2013 Corporate and Other Bonds [Member]	Sep. 30, 2014 Corporate and Other Bonds [Member]	Sep. 30, 2013 Corporate and Other Bonds [Member]	Sep. 30, 2014 States, Municipalities and Political Subdivisions [Member]	Sep. 30, 2013 States, Municipalities and Political Subdivisions [Member]	Sep. 30, 2014 States, Municipalities and Political Subdivisions [Member]	Sep. 30, 2013 States, Municipalities and Political Subdivisions [Member]	Sep. 30, 2014 Residential Mortgage-Backed [Member]	Sep. 30, 2013 Residential Mortgage-Backed [Member]	Sep. 30, 2014 Residential Mortgage-Backed [Member]	Sep. 30, 2013 Residential Mortgage-Backed [Member]	Sep. 30, 2014 Commercial Mortgage-Backed [Member]	Sep. 30, 2013 Commercial Mortgage-Backed [Member]	Sep. 30, 2014 Commercial Mortgage-Backed [Member]	Sep. 30, 2013 Commercial Mortgage-Backed [Member]	Sep. 30, 2014 Other Asset-Backed [Member]	Sep. 30, 2013 Other Asset-Backed [Member]	Sep. 30, 2014 Other Asset-Backed [Member]	Sep. 30, 2013 Other Asset-Backed [Member]	Sep. 30, 2014 Total Asset-Backed [Member]	Sep. 30, 2013 Total Asset-Backed [Member]	Sep. 30, 2014 Total Asset-Backed [Member]	Sep. 30, 2013 Total Asset-Backed [Member]	Sep. 30, 2013 Redeemable Preferred Stock [Member]	Sep. 30, 2013 Redeemable Preferred Stock [Member]	Sep. 30, 2014 Total Fixed Maturities Available-for-Sale [Member]	Sep. 30, 2013 Total Fixed Maturities Available-for-Sale [Member]	Sep. 30, 2014 Total Fixed Maturities Available-for-Sale [Member]	Sep. 30, 2013 Total Fixed Maturities Available-for-Sale [Member]	Sep. 30, 2013 Fixed Maturities, Trading [Member]	Sep. 30, 2014 Fixed Maturities, Trading [Member]	Sep. 30, 2013 Fixed Maturities, Trading [Member]	Jun. 30, 2014 Fixed Maturities, Trading [Member]	Sep. 30, 2014 Fixed Maturity Securities [Member]	Sep. 30, 2013 Fixed Maturity Securities [Member]	Sep. 30, 2014 Fixed Maturity Securities [Member]	Sep. 30, 2013 Fixed Maturity Securities [Member]	Sep. 30, 2014 Total Equity Securities Available-for-Sale [Member]	Sep. 30, 2013 Total Equity Securities Available-for-Sale [Member]	Sep. 30, 2014 Total Equity Securities Available-for-Sale [Member]	Sep. 30, 2013 Total Equity Securities Available-for-Sale [Member]	Sep. 30, 2014 Equity Securities, Trading [Member]	Sep. 30, 2014 Equity Securities, Trading [Member]	Sep. 30, 2013 Equity Securities, Trading [Member]	Jun. 30, 2013 Equity Securities, Trading [Member]	Sep. 30, 2014 Equity Securities [Member]	Sep. 30, 2013 Equity Securities [Member]	Sep. 30, 2014 Equity Securities [Member]	Sep. 30, 2013 Equity Securities [Member]	Sep. 30, 2013 Short Term Investments [Member]	Sep. 30, 2013 Other Invested Assets [Member]	Sep. 30, 2014 Life Settlement Contracts [Member]	Sep. 30, 2013 Life Settlement Contracts [Member]	Sep. 30, 2014 Life Settlement Contracts [Member]	Sep. 30, 2013 Life Settlement Contracts [Member]	Sep. 30, 2014 Separate Account Business [Member]	Sep. 30, 2013 Separate Account Business [Member]	Jun. 30, 2013 Separate Account Business [Member]	Dec. 31, 2012 Separate Account Business [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		$ 5	$ (3)	$ 5	$ 194	$ 202	$ 204	$ 219	$ 79	$ 140	$ 71	$ 96	$ 185	$ 428	$ 331	$ 413	$ 59	$ 165	$ 151	$ 129	$ 626	$ 387	$ 446	$ 368	$ 870	$ 980	$ 928	$ 910	$ 25	$ 26	$ 1,143	$ 1,347	$ 1,203	$ 1,251	$ 87	$ 80	$ 89	$ 91	$ 1,234	$ 1,434	$ 1,283	$ 1,340	$ 2	$ 13	$ 11	$ 34	$ 4	$ 8	$ 7	$ 2	$ 6	$ 15	$ 19	$ 41	$ 6	$ 1	$ 86	$ 91	$ 88	$ 100	$ 1	$ 2	$ 2	$ 2
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in Net Income		2	1	7		1	2	2			1	(3)	1		(22)	2	2	(1)	4		1		2	3	4	(1)	(16)	5	(1)	(1)	4	(1)	(13)	3	(8)	11	(7)		4	(9)	(2)	(4)		(2)	3	(22)			(5)			(2)	3	(27)			1	3	23	14
Net Realized Gains (Losses) and Net Change in Unrealized Gains (Losses), Included in OCI		(4)		(6)	(1)			(1)	1	(3)	3	1		(20)	62	(21)	(2)	(2)	(2)	7	(4)	1		(1)	(6)	(21)	60	(15)	1		(6)	(23)	63	(15)					(6)	(23)	63	(15)	(1)	2	(5)	2					(1)	2	(5)	2
Purchases			(2)	1	4	6	30	129			1	122		5	47	116	28	10	28	88	80	56	457	230	108	71	532	434			112	77	563	685					112	77	563	685	16		16		(1)	1			15		17
Sales		(2)	2	(2)		(6)	(10)	(96)			(10)	(79)			(174)	(10)			(60)				(111)	(132)			(345)	(142)				(6)	(365)	(317)	(1)		(4)			(7)	(365)	(321)			(8)			(6)					(14)		(6)	(1)
Settlements		(1)		(5)	(3)	(8)	(13)	(34)		(15)		(20)	(17)	(21)	(57)	(53)	(21)	(1)	(23)	(10)	(25)	(6)	(115)	(30)	(63)	(28)	(195)	(93)	(25)	(25)	(66)	(76)	(208)	(172)					(66)	(76)	(208)	(172)															(1)	(4)	(25)	(24)
Transfers into Level 3						17	8	43			14	5	11		32	4	31		43	21					42		75	25			42	17	97	73					42	17	97	73
Transfers out of Level 3			2		(21)	(1)	(48)	(51)		(27)		(27)	(20)	(22)	(59)	(81)		(14)	(44)	(78)	(36)	(5)	(37)	(5)	(56)	(41)	(140)	(164)			(77)	(69)	(188)	(242)					(77)	(69)	(188)	(242)				(1)								(1)							(1)
Ending balance					173	211	173	211	80	95	80	95	160	370	160	370	97	157	97	157	642	433	642	433	899	960	899	960			1,152	1,266	1,152	1,266	78	91	78	91	1,243	1,344	1,243	1,344	17	13	17	13	3	3	2	2	20	15	20	15			86	90	86	90		2	2	2
Unrealized Gains (Losses) Recognized in Net Income on Level 3 Assets and Liabilities Held at September 30	$ (1)		$ 1	$ 1				$ (2)						$ (1)		$ (3)						$ (1)	$ (1)	$ (2)		$ (2)	$ (1)	$ (5)				$ (2)	$ (1)	$ (7)	$ (8)	$ 11	$ (7)			$ (10)	$ 10	$ (14)		$ (2)		$ (22)			$ (5)			$ (2)		$ (27)			$ 1		$ 3	$ (1)