Investments - Amortized Cost and Fair Values of Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	$ 39,518	$ 38,231
Gross Unrealized Gains	2,807	2,773
Gross Unrealized Losses	282	551
Estimated Fair Value	42,043	40,453
Unrealized OTTI Losses (Gains)	(45)	(41)
Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	38,947	37,407
Gross Unrealized Gains	2,739	2,707
Gross Unrealized Losses	192	413
Estimated Fair Value	41,494	39,701
Unrealized OTTI Losses (Gains)	(45)	(41)
Corporate and Other Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	17,711	17,097
Gross Unrealized Gains	1,323	1,019
Gross Unrealized Losses	76	347
Estimated Fair Value	18,958	17,769
Unrealized OTTI Losses (Gains)	(1)
States, Municipalities and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	12,060	11,729
Gross Unrealized Gains	1,213	1,453
Gross Unrealized Losses	33	8
Estimated Fair Value	13,240	13,174
Unrealized OTTI Losses (Gains)	(16)	(4)
Residential Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	5,004	4,935
Gross Unrealized Gains	120	154
Gross Unrealized Losses	51	17
Estimated Fair Value	5,073	5,072
Unrealized OTTI Losses (Gains)	(28)	(37)
Commercial Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	2,016	2,154
Gross Unrealized Gains	48	55
Gross Unrealized Losses	24	12
Estimated Fair Value	2,040	2,197
Other Asset-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	1,022	923
Gross Unrealized Gains	8	6
Gross Unrealized Losses	5	8
Estimated Fair Value	1,025	921
Total Asset-Backed [Member] | Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	8,042	8,012
Gross Unrealized Gains	176	215
Gross Unrealized Losses	80	37
Estimated Fair Value	8,138	8,190
Unrealized OTTI Losses (Gains)	(28)	(37)
U.S. Treasury and Obligations of Government-Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	83	62
Gross Unrealized Gains	10	5
Estimated Fair Value	93	67
Foreign Government [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	435	334
Gross Unrealized Gains	13	13
Gross Unrealized Losses	3	1
Estimated Fair Value	445	346
Redeemable Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	18	33
Gross Unrealized Gains	1	2
Estimated Fair Value	19	35
Total Fixed Maturities Available-for-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	38,349	37,267
Gross Unrealized Gains	2,736	2,707
Gross Unrealized Losses	192	393
Estimated Fair Value	40,893	39,581
Unrealized OTTI Losses (Gains)	(45)	(41)
Fixed Maturities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	598	140
Gross Unrealized Gains	3
Gross Unrealized Losses		20
Estimated Fair Value	601	120
Common Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	13	46
Gross Unrealized Gains	6	3
Gross Unrealized Losses		1
Estimated Fair Value	19	48
Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	93	145
Gross Unrealized Gains	2	7
Gross Unrealized Losses	4	3
Estimated Fair Value	91	149
Equity Securities Available-for-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	106	191
Gross Unrealized Gains	8	10
Gross Unrealized Losses	4	4
Estimated Fair Value	110	197
Equity Securities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	465	633
Gross Unrealized Gains	60	56
Gross Unrealized Losses	86	134
Estimated Fair Value	439	555
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	571	824
Gross Unrealized Gains	68	66
Gross Unrealized Losses	90	138
Estimated Fair Value	$ 549	$ 752