Investments - Securities Available-for-Sale in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Corporate and Other Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 4,882	$ 1,330
Gross Unrealized Losses, Less than 12 Months	302	46
Estimated Fair Value, 12 Months or Longer	174	277
Gross Unrealized Losses, 12 Months or Longer	45	15
Total Estimated Fair Value	5,056	1,607
Total Gross Unrealized Losses	347	61
States, Municipalities and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	338	335
Gross Unrealized Losses, Less than 12 Months	8	5
Estimated Fair Value, 12 Months or Longer	75	127
Gross Unrealized Losses, 12 Months or Longer		3
Total Estimated Fair Value	413	462
Total Gross Unrealized Losses	8	8
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	963	293
Gross Unrealized Losses, Less than 12 Months	9	5
Estimated Fair Value, 12 Months or Longer	164	189
Gross Unrealized Losses, 12 Months or Longer	8	8
Total Estimated Fair Value	1,127	482
Total Gross Unrealized Losses	17	13
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	652	264
Gross Unrealized Losses, Less than 12 Months	10	2
Estimated Fair Value, 12 Months or Longer	96	99
Gross Unrealized Losses, 12 Months or Longer	2	3
Total Estimated Fair Value	748	363
Total Gross Unrealized Losses	12	5
Other Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	552	607
Gross Unrealized Losses, Less than 12 Months	8	10
Estimated Fair Value, 12 Months or Longer	5	7
Total Estimated Fair Value	557	614
Total Gross Unrealized Losses	8	10
Total Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,167	1,164
Gross Unrealized Losses, Less than 12 Months	27	17
Estimated Fair Value, 12 Months or Longer	265	295
Gross Unrealized Losses, 12 Months or Longer	10	11
Total Estimated Fair Value	2,432	1,459
Total Gross Unrealized Losses	37	28
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	3
Estimated Fair Value, 12 Months or Longer		4
Total Estimated Fair Value	4	7
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	54	3
Gross Unrealized Losses, Less than 12 Months	1
Estimated Fair Value, 12 Months or Longer		3
Total Estimated Fair Value	54	6
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	3
Total Estimated Fair Value	3	3
Total Fixed Maturities Available-for-Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	7,448	2,838
Gross Unrealized Losses, Less than 12 Months	338	68
Estimated Fair Value, 12 Months or Longer	514	706
Gross Unrealized Losses, 12 Months or Longer	55	29
Total Estimated Fair Value	7,962	3,544
Total Gross Unrealized Losses	393	97
Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	3
Gross Unrealized Losses, Less than 12 Months	1
Total Estimated Fair Value	3
Total Gross Unrealized Losses	1
Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	13	17
Gross Unrealized Losses, Less than 12 Months	3	2
Estimated Fair Value, 12 Months or Longer		1
Total Estimated Fair Value	13	18
Total Gross Unrealized Losses	3	2
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	7,464	2,855
Gross Unrealized Losses, Less than 12 Months	342	70
Estimated Fair Value, 12 Months or Longer	514	707
Gross Unrealized Losses, 12 Months or Longer	55	29
Total Estimated Fair Value	7,978	3,562
Total Gross Unrealized Losses	$ 397	$ 99