Investments - Securities Available-for-Sale in Gross Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Corporate and Other Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 1,330	$ 3,592
Gross Unrealized Losses, Less than 12 Months	46	129
Estimated Fair Value, 12 Months or Longer	277	72
Gross Unrealized Losses, 12 Months or Longer	15	6
Total Estimated Fair Value	1,607	3,664
Total Gross Unrealized Losses	61	135
States, Municipalities and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	335	3,251
Gross Unrealized Losses, Less than 12 Months	5	197
Estimated Fair Value, 12 Months or Longer	127	129
Gross Unrealized Losses, 12 Months or Longer	3	75
Total Estimated Fair Value	462	3,380
Total Gross Unrealized Losses	8	272
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	293	1,293
Gross Unrealized Losses, Less than 12 Months	5	29
Estimated Fair Value, 12 Months or Longer	189	343
Gross Unrealized Losses, 12 Months or Longer	8	63
Total Estimated Fair Value	482	1,636
Total Gross Unrealized Losses	13	92
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	264	640
Gross Unrealized Losses, Less than 12 Months	2	22
Estimated Fair Value, 12 Months or Longer	99
Gross Unrealized Losses, 12 Months or Longer	3
Total Estimated Fair Value	363	640
Total Gross Unrealized Losses	5	22
Other Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	607	269
Gross Unrealized Losses, Less than 12 Months	10	3
Estimated Fair Value, 12 Months or Longer	7
Total Estimated Fair Value	614	269
Total Gross Unrealized Losses	10	3
Total Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,164	2,202
Gross Unrealized Losses, Less than 12 Months	17	54
Estimated Fair Value, 12 Months or Longer	295	343
Gross Unrealized Losses, 12 Months or Longer	11	63
Total Estimated Fair Value	1,459	2,545
Total Gross Unrealized Losses	28	117
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	3	13
Gross Unrealized Losses, Less than 12 Months		1
Estimated Fair Value, 12 Months or Longer	4
Total Estimated Fair Value	7	13
Total Gross Unrealized Losses		1
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	3	111
Gross Unrealized Losses, Less than 12 Months		3
Estimated Fair Value, 12 Months or Longer	3
Total Estimated Fair Value	6	111
Total Gross Unrealized Losses		3
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	2,838	9,169
Gross Unrealized Losses, Less than 12 Months	68	384
Estimated Fair Value, 12 Months or Longer	706	544
Gross Unrealized Losses, 12 Months or Longer	29	144
Total Estimated Fair Value	3,544	9,713
Total Gross Unrealized Losses	97	528
Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	17	87
Gross Unrealized Losses, Less than 12 Months	2	4
Estimated Fair Value, 12 Months or Longer	1
Total Estimated Fair Value	18	87
Total Gross Unrealized Losses	2	4
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,855	9,256
Gross Unrealized Losses, Less than 12 Months	70	388
Estimated Fair Value, 12 Months or Longer	707	544
Gross Unrealized Losses, 12 Months or Longer	29	144
Total Estimated Fair Value	3,562	9,800
Total Gross Unrealized Losses	$ 99	$ 532