Investments - Securities Available-for-Sale in Gross Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 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	$ 854	$ 1,330
Gross Unrealized Losses, Less than 12 Months	33	46
Estimated Fair Value, 12 Months or Longer	139	277
Gross Unrealized Losses, 12 Months or Longer	12	15
Total Estimated Fair Value	993	1,607
Total Gross Unrealized Losses	45	61
States, Municipalities and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	479	335
Gross Unrealized Losses, Less than 12 Months	6	5
Estimated Fair Value, 12 Months or Longer	100	127
Gross Unrealized Losses, 12 Months or Longer	3	3
Total Estimated Fair Value	579	462
Total Gross Unrealized Losses	9	8
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	318	293
Gross Unrealized Losses, Less than 12 Months	5	5
Estimated Fair Value, 12 Months or Longer	148	189
Gross Unrealized Losses, 12 Months or Longer	8	8
Total Estimated Fair Value	466	482
Total Gross Unrealized Losses	13	13
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	175	264
Gross Unrealized Losses, Less than 12 Months	3	2
Estimated Fair Value, 12 Months or Longer	62	99
Gross Unrealized Losses, 12 Months or Longer	2	3
Total Estimated Fair Value	237	363
Total Gross Unrealized Losses	5	5
Other Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	187	607
Gross Unrealized Losses, Less than 12 Months	1	10
Estimated Fair Value, 12 Months or Longer	5	7
Total Estimated Fair Value	192	614
Total Gross Unrealized Losses	1	10
Total Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	680	1,164
Gross Unrealized Losses, Less than 12 Months	9	17
Estimated Fair Value, 12 Months or Longer	215	295
Gross Unrealized Losses, 12 Months or Longer	10	11
Total Estimated Fair Value	895	1,459
Total Gross Unrealized Losses	19	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	3	3
Estimated Fair Value, 12 Months or Longer		4
Total Estimated Fair Value	3	7
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	13	3
Estimated Fair Value, 12 Months or Longer	1	3
Total Estimated Fair Value	14	6
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	2,029	2,838
Gross Unrealized Losses, Less than 12 Months	48	68
Estimated Fair Value, 12 Months or Longer	455	706
Gross Unrealized Losses, 12 Months or Longer	25	29
Total Estimated Fair Value	2,484	3,544
Total Gross Unrealized Losses	73	97
Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	15	17
Gross Unrealized Losses, Less than 12 Months	4	2
Estimated Fair Value, 12 Months or Longer		1
Total Estimated Fair Value	15	18
Total Gross Unrealized Losses	4	2
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,044	2,855
Gross Unrealized Losses, Less than 12 Months	52	70
Estimated Fair Value, 12 Months or Longer	455	707
Gross Unrealized Losses, 12 Months or Longer	25	29
Total Estimated Fair Value	2,499	3,562
Total Gross Unrealized Losses	$ 77	$ 99