Investments - Securities Available-For-Sale in Gross Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Corporate and other bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 3,478	$ 846
Gross Unrealized Losses, Less than 12 Months	143	13
Estimated Fair Value, 12 Months or Longer	33	108
Gross Unrealized Losses, 12 Months or Longer	4	8
Total Estimated Fair Value	3,511	954
Total Gross Unrealized Losses	147	21
States, municipalities and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,075	254
Gross Unrealized Losses, Less than 12 Months	130	5
Estimated Fair Value, 12 Months or Longer	119	165
Gross Unrealized Losses, 12 Months or Longer	43	39
Total Estimated Fair Value	2,194	419
Total Gross Unrealized Losses	173	44
Residential mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,462	583
Gross Unrealized Losses, Less than 12 Months	33	5
Estimated Fair Value, 12 Months or Longer	321	452
Gross Unrealized Losses, 12 Months or Longer	55	66
Total Estimated Fair Value	1,783	1,035
Total Gross Unrealized Losses	88	71
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	593	85
Gross Unrealized Losses, Less than 12 Months	23	2
Estimated Fair Value, 12 Months or Longer	79	141
Gross Unrealized Losses, 12 Months or Longer	4	15
Total Estimated Fair Value	672	226
Total Gross Unrealized Losses	27	17
Other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	235
Gross Unrealized Losses, Less than 12 Months	2
Total Estimated Fair Value	235
Total Gross Unrealized Losses	2
Total asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,290	668
Gross Unrealized Losses, Less than 12 Months	58	7
Estimated Fair Value, 12 Months or Longer	400	593
Gross Unrealized Losses, 12 Months or Longer	59	81
Total Estimated Fair Value	2,690	1,261
Total Gross Unrealized Losses	117	88
Foreign government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	65
Gross Unrealized Losses, Less than 12 Months	1
Total Estimated Fair Value	65
Total Gross Unrealized Losses	1
Redeemable preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	39	28
Gross Unrealized Losses, Less than 12 Months	2	1
Total Estimated Fair Value	39	28
Total Gross Unrealized Losses	2	1
Fixed maturity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	7,947	1,819
Gross Unrealized Losses, Less than 12 Months	334	27
Estimated Fair Value, 12 Months or Longer	552	866
Gross Unrealized Losses, 12 Months or Longer	106	128
Total Estimated Fair Value	8,499	2,685
Total Gross Unrealized Losses	440	155
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		23
Gross Unrealized Losses, Less than 12 Months		1
Total Estimated Fair Value		23
Total Gross Unrealized Losses		$ 1