Investments - Amortized Cost and Fair Values of Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	$ 38,231	$ 38,202
Gross Unrealized Gains	2,773	3,640
Gross Unrealized Losses	551	229
Estimated Fair Value	40,453	41,613
Unrealized OTTI Losses (Gains)	(41)	(55)
Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	37,407	37,469
Gross Unrealized Gains	2,707	3,530
Gross Unrealized Losses	413	114
Estimated Fair Value	39,701	40,885
Unrealized OTTI Losses (Gains)	(41)	(55)
Corporate and Other Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	17,097	17,226
Gross Unrealized Gains	1,019	1,721
Gross Unrealized Losses	347	61
Estimated Fair Value	17,769	18,886
States, Municipalities and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	11,729	11,285
Gross Unrealized Gains	1,453	1,463
Gross Unrealized Losses	8	8
Estimated Fair Value	13,174	12,740
Unrealized OTTI Losses (Gains)	(4)
Residential Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	4,935	5,028
Gross Unrealized Gains	154	218
Gross Unrealized Losses	17	13
Estimated Fair Value	5,072	5,233
Unrealized OTTI Losses (Gains)	(37)	(53)
Commercial Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	2,154	2,056
Gross Unrealized Gains	55	93
Gross Unrealized Losses	12	5
Estimated Fair Value	2,197	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	923	1,234
Gross Unrealized Gains	6	11
Gross Unrealized Losses	8	10
Estimated Fair Value	921	1,235
Total Asset-Backed [Member] | Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	8,012	8,318
Gross Unrealized Gains	215	322
Gross Unrealized Losses	37	28
Estimated Fair Value	8,190	8,612
Unrealized OTTI Losses (Gains)	(37)	(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	62	26
Gross Unrealized Gains	5	5
Estimated Fair Value	67	31
Foreign Government [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	334	438
Gross Unrealized Gains	13	16
Gross Unrealized Losses	1
Estimated Fair Value	346	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	37,267	37,332
Gross Unrealized Gains	2,707	3,530
Gross Unrealized Losses	393	97
Estimated Fair Value	39,581	40,765
Unrealized OTTI Losses (Gains)	(41)	(55)
Fixed Maturities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	140	137
Gross Unrealized Losses	20	17
Estimated Fair Value	120	120
Common Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	46	38
Gross Unrealized Gains	3	9
Gross Unrealized Losses	1
Estimated Fair Value	48	47
Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	145	172
Gross Unrealized Gains	7	5
Gross Unrealized Losses	3	2
Estimated Fair Value	149	175
Total Equity Securities Available-for-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	191	210
Gross Unrealized Gains	10	14
Gross Unrealized Losses	4	2
Estimated Fair Value	197	222
Equity Securities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	633	523
Gross Unrealized Gains	56	96
Gross Unrealized Losses	134	113
Estimated Fair Value	555	506
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	824	733
Gross Unrealized Gains	66	110
Gross Unrealized Losses	138	115
Estimated Fair Value	$ 752	$ 728