Investments (Securities Available-For-Sale in Gross Unrealized Loss Position) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Corporate And Other Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	$ 600	$ 2,552
Gross unrealized losses, less than 12 months	18	126
Estimated fair value, 12 months or longer	210	159
Gross unrealized losses, 12 months or longer	14	28
Total Estimated Fair Value	810	2,711
Gross Unrealized Losses	32	154
States, Municipalities And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	84	67
Gross unrealized losses, less than 12 months	1	1
Estimated fair value, 12 months or longer	227	721
Gross unrealized losses, 12 months or longer	52	135
Total Estimated Fair Value	311	788
Gross Unrealized Losses	53	136
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	327	719
Gross unrealized losses, less than 12 months	3	36
Estimated fair value, 12 months or longer	580	874
Gross unrealized losses, 12 months or longer	78	147
Total Estimated Fair Value	907	1,593
Gross Unrealized Losses	81	183
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	142	431
Gross unrealized losses, less than 12 months	2	39
Estimated fair value, 12 months or longer	132	169
Gross unrealized losses, 12 months or longer	15	20
Total Estimated Fair Value	274	600
Gross Unrealized Losses	17	59
Other Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	66	389
Gross unrealized losses, less than 12 months	1	4
Total Estimated Fair Value	66	389
Gross Unrealized Losses	1	4
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	535	1,539
Gross unrealized losses, less than 12 months	6	79
Estimated fair value, 12 months or longer	712	1,043
Gross unrealized losses, 12 months or longer	93	167
Total Estimated Fair Value	1,247	2,582
Gross Unrealized Losses	99	246
U.S. Government Agency Or Sponsored Enterprise [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	22
Gross unrealized losses, less than 12 months	1
Total Estimated Fair Value	22
Gross Unrealized Losses	1
Fixed Maturities Available-For-Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months		4,158
Gross unrealized losses, less than 12 months		206
Estimated fair value, 12 months or longer		1,923
Gross unrealized losses, 12 months or longer		330
Total Estimated Fair Value		6,081
Gross Unrealized Losses		536
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months	1,241	4,275
Gross unrealized losses, less than 12 months	26	211
Estimated fair value, 12 months or longer	1,149	1,923
Gross unrealized losses, 12 months or longer	159	330
Total Estimated Fair Value	2,390	6,198
Gross Unrealized Losses	185	541
Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value, less than 12 months		117
Gross unrealized losses, less than 12 months		5
Total Estimated Fair Value		117
Gross Unrealized Losses		$ 5