Investments - Securities Available-for-Sale in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Corporate and Other Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 1,032	$ 4,882
Gross Unrealized Losses, Less than 12 Months	43	302
Estimated Fair Value, 12 Months or Longer	562	174
Gross Unrealized Losses, 12 Months or Longer	50	45
Total Estimated Fair Value	1,594	5,056
Total Gross Unrealized Losses	93	347
States, Municipalities and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	68	338
Gross Unrealized Losses, Less than 12 Months	2	8
Estimated Fair Value, 12 Months or Longer	10	75
Total Estimated Fair Value	78	413
Total Gross Unrealized Losses	2	8
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	293	963
Gross Unrealized Losses, Less than 12 Months	8	9
Estimated Fair Value, 12 Months or Longer	234	164
Gross Unrealized Losses, 12 Months or Longer	12	8
Total Estimated Fair Value	527	1,127
Total Gross Unrealized Losses	20	17
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	386	652
Gross Unrealized Losses, Less than 12 Months	7	10
Estimated Fair Value, 12 Months or Longer	118	96
Gross Unrealized Losses, 12 Months or Longer	1	2
Total Estimated Fair Value	504	748
Total Gross Unrealized Losses	8	12
Other Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	306	552
Gross Unrealized Losses, Less than 12 Months	5	8
Estimated Fair Value, 12 Months or Longer	5	5
Total Estimated Fair Value	311	557
Total Gross Unrealized Losses	5	8
Total Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	985	2,167
Gross Unrealized Losses, Less than 12 Months	20	27
Estimated Fair Value, 12 Months or Longer	357	265
Gross Unrealized Losses, 12 Months or Longer	13	10
Total Estimated Fair Value	1,342	2,432
Total Gross Unrealized Losses	33	37
U.S. Treasury and Obligations of Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months		4
Total Estimated Fair Value		4
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	8	54
Gross Unrealized Losses, Less than 12 Months		1
Estimated Fair Value, 12 Months or Longer	5
Total Estimated Fair Value	13	54
Total Gross Unrealized Losses		1
Redeemable Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months		3
Total Estimated Fair Value		3
Total Fixed Maturities Available-for-Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,093	7,448
Gross Unrealized Losses, Less than 12 Months	65	338
Estimated Fair Value, 12 Months or Longer	934	514
Gross Unrealized Losses, 12 Months or Longer	63	55
Total Estimated Fair Value	3,027	7,962
Total Gross Unrealized Losses	128	393
Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	4	3
Gross Unrealized Losses, Less than 12 Months	2	1
Total Estimated Fair Value	4	3
Total Gross Unrealized Losses	2	1
Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	23	13
Gross Unrealized Losses, Less than 12 Months	3	3
Total Estimated Fair Value	23	13
Total Gross Unrealized Losses	3	3
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,120	7,464
Gross Unrealized Losses, Less than 12 Months	70	342
Estimated Fair Value, 12 Months or Longer	934	514
Gross Unrealized Losses, 12 Months or Longer	63	55
Total Estimated Fair Value	3,054	7,978
Total Gross Unrealized Losses	$ 133	$ 397