Investments - Securities Available-for-Sale in Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Corporate and Other Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 2,615	$ 4,882
Gross Unrealized Losses, Less than 12 Months	61	302
Estimated Fair Value, 12 Months or Longer	254	174
Gross Unrealized Losses, 12 Months or Longer	15	45
Total Estimated Fair Value	2,869	5,056
Total Gross Unrealized Losses	76	347
States, Municipalities and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	959	338
Gross Unrealized Losses, Less than 12 Months	32	8
Estimated Fair Value, 12 Months or Longer	23	75
Gross Unrealized Losses, 12 Months or Longer	1
Total Estimated Fair Value	982	413
Total Gross Unrealized Losses	33	8
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,136	963
Gross Unrealized Losses, Less than 12 Months	44	9
Estimated Fair Value, 12 Months or Longer	201	164
Gross Unrealized Losses, 12 Months or Longer	7	8
Total Estimated Fair Value	2,337	1,127
Total Gross Unrealized Losses	51	17
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	756	652
Gross Unrealized Losses, Less than 12 Months	22	10
Estimated Fair Value, 12 Months or Longer	69	96
Gross Unrealized Losses, 12 Months or Longer	2	2
Total Estimated Fair Value	825	748
Total Gross Unrealized Losses	24	12
Other Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	398	552
Gross Unrealized Losses, Less than 12 Months	5	8
Estimated Fair Value, 12 Months or Longer	24	5
Total Estimated Fair Value	422	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	3,290	2,167
Gross Unrealized Losses, Less than 12 Months	71	27
Estimated Fair Value, 12 Months or Longer	294	265
Gross Unrealized Losses, 12 Months or Longer	9	10
Total Estimated Fair Value	3,584	2,432
Total Gross Unrealized Losses	80	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	5	4
Total Estimated Fair Value	5	4
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	108	54
Gross Unrealized Losses, Less than 12 Months	3	1
Total Estimated Fair Value	108	54
Total Gross Unrealized Losses	3	1
Total Fixed Maturities Available-for-Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	6,977	7,448
Gross Unrealized Losses, Less than 12 Months	167	338
Estimated Fair Value, 12 Months or Longer	571	514
Gross Unrealized Losses, 12 Months or Longer	25	55
Total Estimated Fair Value	7,548	7,962
Total Gross Unrealized Losses	192	393
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	12	16
Gross Unrealized Losses, Less than 12 Months		4
Estimated Fair Value, 12 Months or Longer	13
Gross Unrealized Losses, 12 Months or Longer	4
Total Estimated Fair Value	25	16
Total Gross Unrealized Losses	4	4
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	6,989	7,464
Gross Unrealized Losses, Less than 12 Months	167	342
Estimated Fair Value, 12 Months or Longer	584	514
Gross Unrealized Losses, 12 Months or Longer	29	55
Total Estimated Fair Value	7,573	7,978
Total Gross Unrealized Losses	$ 196	397
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
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
Gross Unrealized Losses, Less than 12 Months		3
Total Estimated Fair Value		13
Total Gross Unrealized Losses		$ 3