Investments - Amortized Cost and Fair Values of Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	$ 38,668	$ 38,202
Gross Unrealized Gains	2,942	3,640
Gross Unrealized Losses	424	229
Estimated Fair Value	41,186	41,613
Unrealized OTTI Losses (Gains)	(51)	(55)
Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	37,690	37,469
Gross Unrealized Gains	2,884	3,530
Gross Unrealized Losses	273	114
Estimated Fair Value	40,301	40,885
Unrealized OTTI Losses (Gains)	(51)	(55)
Corporate and Other Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	17,172	17,226
Gross Unrealized Gains	1,237	1,721
Gross Unrealized Losses	210	61
Estimated Fair Value	18,199	18,886
States, Municipalities and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	11,978	11,285
Gross Unrealized Gains	1,336	1,463
Gross Unrealized Losses	17	8
Estimated Fair Value	13,297	12,740
Unrealized OTTI Losses (Gains)	(5)
Residential Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	4,850	5,028
Gross Unrealized Gains	204	218
Gross Unrealized Losses	13	13
Estimated Fair Value	5,041	5,233
Unrealized OTTI Losses (Gains)	(46)	(53)
Commercial Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	2,183	2,056
Gross Unrealized Gains	77	93
Gross Unrealized Losses	9	5
Estimated Fair Value	2,251	2,144
Unrealized OTTI Losses (Gains)		(2)
Other Asset-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	1,009	1,234
Gross Unrealized Gains	11	11
Gross Unrealized Losses	4	10
Estimated Fair Value	1,016	1,235
Total Asset-Backed [Member] | Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	8,042	8,318
Gross Unrealized Gains	292	322
Gross Unrealized Losses	26	28
Estimated Fair Value	8,308	8,612
Unrealized OTTI Losses (Gains)	(46)	(55)
U.S. Treasury and Obligations of Government-Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	24	26
Gross Unrealized Gains	5	5
Estimated Fair Value	29	31
Foreign Government [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	333	438
Gross Unrealized Gains	12	16
Gross Unrealized Losses	1
Estimated Fair Value	344	454
Redeemable Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	33	39
Gross Unrealized Gains	2	3
Estimated Fair Value	35	42
Total Fixed Maturities Available-for-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	37,582	37,332
Gross Unrealized Gains	2,884	3,530
Gross Unrealized Losses	254	97
Estimated Fair Value	40,212	40,765
Unrealized OTTI Losses (Gains)	(51)	(55)
Fixed Maturities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	108	137
Gross Unrealized Losses	19	17
Estimated Fair Value	89	120
Common Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	62	38
Gross Unrealized Gains	3	9
Estimated Fair Value	65	47
Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	145	172
Gross Unrealized Gains	4	5
Gross Unrealized Losses	2	2
Estimated Fair Value	147	175
Total Equity Securities Available-for-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	207	210
Gross Unrealized Gains	7	14
Gross Unrealized Losses	2	2
Estimated Fair Value	212	222
Equity Securities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	771	523
Gross Unrealized Gains	51	96
Gross Unrealized Losses	149	113
Estimated Fair Value	673	506
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	978	733
Gross Unrealized Gains	58	110
Gross Unrealized Losses	151	115
Estimated Fair Value	$ 885	$ 728